RFC 3501: INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1

This RFC is now obsolete

This RFC was updated

Network Working Group M. Crispin
Request for Comments: 3501 University of Washington
Obsoletes: 2060 March 2003
Category: Standards Track


 INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements. Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

 The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1)
 allows a client to access and manipulate electronic mail messages on
 a server. IMAP4rev1 permits manipulation of mailboxes (remote
 message folders) in a way that is functionally equivalent to local
 folders. IMAP4rev1 also provides the capability for an offline
 client to resynchronize with the server.

 IMAP4rev1 includes operations for creating, deleting, and renaming
 mailboxes, checking for new messages, permanently removing messages,
 setting and clearing flags, RFC 2822 and RFC 2045 parsing, searching,
 and selective fetching of message attributes, texts, and portions
 thereof. Messages in IMAP4rev1 are accessed by the use of numbers.
 These numbers are either message sequence numbers or unique
 identifiers.

 IMAP4rev1 supports a single server. A mechanism for accessing
 configuration information to support multiple IMAP4rev1 servers is
 discussed in RFC 2244.

 IMAP4rev1 does not specify a means of posting mail; this function is
 handled by a mail transfer protocol such as RFC 2821.








Crispin Standards Track [Page 1]

RFC 3501 IMAPv4 March 2003


Table of Contents

 IMAP4rev1 Protocol Specification ................................ 4
 1. How to Read This Document ............................... 4
 1.1. Organization of This Document ........................... 4
 1.2. Conventions Used in This Document ....................... 4
 1.3. Special Notes to Implementors ........................... 5
 2. Protocol Overview ....................................... 6
 2.1. Link Level .............................................. 6
 2.2. Commands and Responses .................................. 6
 2.2.1. Client Protocol Sender and Server Protocol Receiver ..... 6
 2.2.2. Server Protocol Sender and Client Protocol Receiver ..... 7
 2.3. Message Attributes ...................................... 8
 2.3.1. Message Numbers ......................................... 8
 2.3.1.1. Unique Identifier (UID) Message Attribute ....... 8
 2.3.1.2. Message Sequence Number Message Attribute ....... 10
 2.3.2. Flags Message Attribute ................................. 11
 2.3.3. Internal Date Message Attribute ......................... 12
 2.3.4. [RFC-2822] Size Message Attribute ....................... 12
 2.3.5. Envelope Structure Message Attribute .................... 12
 2.3.6. Body Structure Message Attribute ........................ 12
 2.4. Message Texts ........................................... 13
 3. State and Flow Diagram .................................. 13
 3.1. Not Authenticated State ................................. 13
 3.2. Authenticated State ..................................... 13
 3.3. Selected State .......................................... 13
 3.4. Logout State ............................................ 14
 4. Data Formats ............................................ 16
 4.1. Atom .................................................... 16
 4.2. Number .................................................. 16
 4.3. String .................................................. 16
 4.3.1. 8-bit and Binary Strings ................................ 17
 4.4. Parenthesized List ...................................... 17
 4.5. NIL ..................................................... 17
 5. Operational Considerations .............................. 18
 5.1. Mailbox Naming .......................................... 18
 5.1.1. Mailbox Hierarchy Naming ................................ 19
 5.1.2. Mailbox Namespace Naming Convention ..................... 19
 5.1.3. Mailbox International Naming Convention ................. 19
 5.2. Mailbox Size and Message Status Updates ................. 21
 5.3. Response when no Command in Progress .................... 21
 5.4. Autologout Timer ........................................ 22
 5.5. Multiple Commands in Progress ........................... 22
 6. Client Commands ........................................ 23
 6.1. Client Commands - Any State ............................ 24
 6.1.1. CAPABILITY Command ..................................... 24
 6.1.2. NOOP Command ........................................... 25
 6.1.3. LOGOUT Command ......................................... 26



Crispin Standards Track [Page 2]

RFC 3501 IMAPv4 March 2003


 6.2. Client Commands - Not Authenticated State .............. 26
 6.2.1. STARTTLS Command ....................................... 27
 6.2.2. AUTHENTICATE Command ................................... 28
 6.2.3. LOGIN Command .......................................... 30
 6.3. Client Commands - Authenticated State .................. 31
 6.3.1. SELECT Command ......................................... 32
 6.3.2. EXAMINE Command ........................................ 34
 6.3.3. CREATE Command ......................................... 34
 6.3.4. DELETE Command ......................................... 35
 6.3.5. RENAME Command ......................................... 37
 6.3.6. SUBSCRIBE Command ...................................... 39
 6.3.7. UNSUBSCRIBE Command .................................... 39
 6.3.8. LIST Command ........................................... 40
 6.3.9. LSUB Command ........................................... 43
 6.3.10. STATUS Command ......................................... 44
 6.3.11. APPEND Command ......................................... 46
 6.4. Client Commands - Selected State ....................... 47
 6.4.1. CHECK Command .......................................... 47
 6.4.2. CLOSE Command .......................................... 48
 6.4.3. EXPUNGE Command ........................................ 49
 6.4.4. SEARCH Command ......................................... 49
 6.4.5. FETCH Command .......................................... 54
 6.4.6. STORE Command .......................................... 58
 6.4.7. COPY Command ........................................... 59
 6.4.8. UID Command ............................................ 60
 6.5. Client Commands - Experimental/Expansion ............... 62
 6.5.1. X<atom> Command ........................................ 62
 7. Server Responses ....................................... 62
 7.1. Server Responses - Status Responses .................... 63
 7.1.1. OK Response ............................................ 65
 7.1.2. NO Response ............................................ 66
 7.1.3. BAD Response ........................................... 66
 7.1.4. PREAUTH Response ....................................... 67
 7.1.5. BYE Response ........................................... 67
 7.2. Server Responses - Server and Mailbox Status ........... 68
 7.2.1. CAPABILITY Response .................................... 68
 7.2.2. LIST Response .......................................... 69
 7.2.3. LSUB Response .......................................... 70
 7.2.4 STATUS Response ........................................ 70
 7.2.5. SEARCH Response ........................................ 71
 7.2.6. FLAGS Response ......................................... 71
 7.3. Server Responses - Mailbox Size ........................ 71
 7.3.1. EXISTS Response ........................................ 71
 7.3.2. RECENT Response ........................................ 72
 7.4. Server Responses - Message Status ...................... 72
 7.4.1. EXPUNGE Response ....................................... 72
 7.4.2. FETCH Response ......................................... 73
 7.5. Server Responses - Command Continuation Request ........ 79



Crispin Standards Track [Page 3]

RFC 3501 IMAPv4 March 2003


 8. Sample IMAP4rev1 connection ............................ 80
 9. Formal Syntax .......................................... 81
 10. Author's Note .......................................... 92
 11. Security Considerations ................................ 92
 11.1. STARTTLS Security Considerations ....................... 92
 11.2. Other Security Considerations .......................... 93
 12. IANA Considerations .................................... 94
 Appendices ..................................................... 95
 A. References ............................................. 95
 B. Changes from RFC 2060 .................................. 97
 C. Key Word Index ......................................... 103
 Author's Address ............................................... 107
 Full Copyright Statement ....................................... 108

IMAP4rev1 Protocol Specification

1. How to Read This Document

1.1. Organization of This Document

 This document is written from the point of view of the implementor of
 an IMAP4rev1 client or server. Beyond the protocol overview in
 section 2, it is not optimized for someone trying to understand the
 operation of the protocol. The material in sections 3 through 5
 provides the general context and definitions with which IMAP4rev1
 operates.

 Sections 6, 7, and 9 describe the IMAP commands, responses, and
 syntax, respectively. The relationships among these are such that it
 is almost impossible to understand any of them separately. In
 particular, do not attempt to deduce command syntax from the command
 section alone; instead refer to the Formal Syntax section.

1.2. Conventions Used in This Document

 "Conventions" are basic principles or procedures. Document
 conventions are noted in this section.

 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
 be interpreted as described in [KEYWORDS].

 The word "can" (not "may") is used to refer to a possible
 circumstance or situation, as opposed to an optional facility of the
 protocol.



Crispin Standards Track [Page 4]

RFC 3501 IMAPv4 March 2003


 "User" is used to refer to a human user, whereas "client" refers to
 the software being run by the user.

 "Connection" refers to the entire sequence of client/server
 interaction from the initial establishment of the network connection
 until its termination.

 "Session" refers to the sequence of client/server interaction from
 the time that a mailbox is selected (SELECT or EXAMINE command) until
 the time that selection ends (SELECT or EXAMINE of another mailbox,
 CLOSE command, or connection termination).

 Characters are 7-bit US-ASCII unless otherwise specified. Other
 character sets are indicated using a "CHARSET", as described in
 [MIME-IMT] and defined in [CHARSET]. CHARSETs have important
 additional semantics in addition to defining character set; refer to
 these documents for more detail.

 There are several protocol conventions in IMAP. These refer to
 aspects of the specification which are not strictly part of the IMAP
 protocol, but reflect generally-accepted practice. Implementations
 need to be aware of these conventions, and avoid conflicts whether or
 not they implement the convention. For example, "&" may not be used
 as a hierarchy delimiter since it conflicts with the Mailbox
 International Naming Convention, and other uses of "&" in mailbox
 names are impacted as well.

1.3. Special Notes to Implementors

 Implementors of the IMAP protocol are strongly encouraged to read the
 IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in
 conjunction with this document, to help understand the intricacies of
 this protocol and how best to build an interoperable product.

 IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
 unpublished IMAP2bis protocols. IMAP4rev1 is largely compatible with
 the IMAP4 protocol described in RFC 1730; the exception being in
 certain facilities added in RFC 1730 that proved problematic and were
 subsequently removed. In the course of the evolution of IMAP4rev1,
 some aspects in the earlier protocols have become obsolete. Obsolete
 commands, responses, and data formats which an IMAP4rev1
 implementation can encounter when used with an earlier implementation
 are described in [IMAP-OBSOLETE].

 Other compatibility issues with IMAP2bis, the most common variant of
 the earlier protocol, are discussed in [IMAP-COMPAT]. A full
 discussion of compatibility issues with rare (and presumed extinct)




Crispin Standards Track [Page 5]

RFC 3501 IMAPv4 March 2003


 variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
 primarily of historical interest.

 IMAP was originally developed for the older [RFC-822] standard, and
 as a consequence several fetch items in IMAP incorporate "RFC822" in
 their name. With the exception of RFC822.SIZE, there are more modern
 replacements; for example, the modern version of RFC822.HEADER is
 BODY.PEEK[HEADER]. In all cases, "RFC822" should be interpreted as a
 reference to the updated [RFC-2822] standard.

2. Protocol Overview

2.1. Link Level

 The IMAP4rev1 protocol assumes a reliable data stream such as that
 provided by TCP. When TCP is used, an IMAP4rev1 server listens on
 port 143.

2.2. Commands and Responses

 An IMAP4rev1 connection consists of the establishment of a
 client/server network connection, an initial greeting from the
 server, and client/server interactions. These client/server
 interactions consist of a client command, server data, and a server
 completion result response.

 All interactions transmitted by client and server are in the form of
 lines, that is, strings that end with a CRLF. The protocol receiver
 of an IMAP4rev1 client or server is either reading a line, or is
 reading a sequence of octets with a known count followed by a line.

2.2.1. Client Protocol Sender and Server Protocol Receiver

 The client command begins an operation. Each client command is
 prefixed with an identifier (typically a short alphanumeric string,
 e.g., A0001, A0002, etc.) called a "tag". A different tag is
 generated by the client for each command.

 Clients MUST follow the syntax outlined in this specification
 strictly. It is a syntax error to send a command with missing or
 extraneous spaces or arguments.

 There are two cases in which a line from the client does not
 represent a complete command. In one case, a command argument is
 quoted with an octet count (see the description of literal in String
 under Data Formats); in the other case, the command arguments require
 server feedback (see the AUTHENTICATE command). In either case, the




Crispin Standards Track [Page 6]

RFC 3501 IMAPv4 March 2003


 server sends a command continuation request response if it is ready
 for the octets (if appropriate) and the remainder of the command.
 This response is prefixed with the token "+".

 Note: If instead, the server detected an error in the
 command, it sends a BAD completion response with a tag
 matching the command (as described below) to reject the
 command and prevent the client from sending any more of the
 command.

 It is also possible for the server to send a completion
 response for some other command (if multiple commands are
 in progress), or untagged data. In either case, the
 command continuation request is still pending; the client
 takes the appropriate action for the response, and reads
 another response from the server. In all cases, the client
 MUST send a complete command (including receiving all
 command continuation request responses and command
 continuations for the command) before initiating a new
 command.

 The protocol receiver of an IMAP4rev1 server reads a command line
 from the client, parses the command and its arguments, and transmits
 server data and a server command completion result response.

2.2.2. Server Protocol Sender and Client Protocol Receiver

 Data transmitted by the server to the client and status responses
 that do not indicate command completion are prefixed with the token
 "*", and are called untagged responses.

 Server data MAY be sent as a result of a client command, or MAY be
 sent unilaterally by the server. There is no syntactic difference
 between server data that resulted from a specific command and server
 data that were sent unilaterally.

 The server completion result response indicates the success or
 failure of the operation. It is tagged with the same tag as the
 client command which began the operation. Thus, if more than one
 command is in progress, the tag in a server completion response
 identifies the command to which the response applies. There are
 three possible server completion responses: OK (indicating success),
 NO (indicating failure), or BAD (indicating a protocol error such as
 unrecognized command or command syntax error).

 Servers SHOULD enforce the syntax outlined in this specification
 strictly. Any client command with a protocol syntax error, including
 (but not limited to) missing or extraneous spaces or arguments,



Crispin Standards Track [Page 7]

RFC 3501 IMAPv4 March 2003


 SHOULD be rejected, and the client given a BAD server completion
 response.

 The protocol receiver of an IMAP4rev1 client reads a response line
 from the server. It then takes action on the response based upon the
 first token of the response, which can be a tag, a "*", or a "+".

 A client MUST be prepared to accept any server response at all times.
 This includes server data that was not requested. Server data SHOULD
 be recorded, so that the client can reference its recorded copy
 rather than sending a command to the server to request the data. In
 the case of certain server data, the data MUST be recorded.

 This topic is discussed in greater detail in the Server Responses
 section.

2.3. Message Attributes

 In addition to message text, each message has several attributes
 associated with it. These attributes can be retrieved individually
 or in conjunction with other attributes or message texts.

2.3.1. Message Numbers

 Messages in IMAP4rev1 are accessed by one of two numbers; the unique
 identifier or the message sequence number.


2.3.1.1. Unique Identifier (UID) Message Attribute

 A 32-bit value assigned to each message, which when used with the
 unique identifier validity value (see below) forms a 64-bit value
 that MUST NOT refer to any other message in the mailbox or any
 subsequent mailbox with the same name forever. Unique identifiers
 are assigned in a strictly ascending fashion in the mailbox; as each
 message is added to the mailbox it is assigned a higher UID than the
 message(s) which were added previously. Unlike message sequence
 numbers, unique identifiers are not necessarily contiguous.

 The unique identifier of a message MUST NOT change during the
 session, and SHOULD NOT change between sessions. Any change of
 unique identifiers between sessions MUST be detectable using the
 UIDVALIDITY mechanism discussed below. Persistent unique identifiers
 are required for a client to resynchronize its state from a previous
 session with the server (e.g., disconnected or offline access
 clients); this is discussed further in [IMAP-DISC].





Crispin Standards Track [Page 8]

RFC 3501 IMAPv4 March 2003


 Associated with every mailbox are two values which aid in unique
 identifier handling: the next unique identifier value and the unique
 identifier validity value.

 The next unique identifier value is the predicted value that will be
 assigned to a new message in the mailbox. Unless the unique
 identifier validity also changes (see below), the next unique
 identifier value MUST have the following two characteristics. First,
 the next unique identifier value MUST NOT change unless new messages
 are added to the mailbox; and second, the next unique identifier
 value MUST change whenever new messages are added to the mailbox,
 even if those new messages are subsequently expunged.

 Note: The next unique identifier value is intended to
 provide a means for a client to determine whether any
 messages have been delivered to the mailbox since the
 previous time it checked this value. It is not intended to
 provide any guarantee that any message will have this
 unique identifier. A client can only assume, at the time
 that it obtains the next unique identifier value, that
 messages arriving after that time will have a UID greater
 than or equal to that value.

 The unique identifier validity value is sent in a UIDVALIDITY
 response code in an OK untagged response at mailbox selection time.
 If unique identifiers from an earlier session fail to persist in this
 session, the unique identifier validity value MUST be greater than
 the one used in the earlier session.

 Note: Ideally, unique identifiers SHOULD persist at all
 times. Although this specification recognizes that failure
 to persist can be unavoidable in certain server
 environments, it STRONGLY ENCOURAGES message store
 implementation techniques that avoid this problem. For
 example:

 1) Unique identifiers MUST be strictly ascending in the
 mailbox at all times. If the physical message store is
 re-ordered by a non-IMAP agent, this requires that the
 unique identifiers in the mailbox be regenerated, since
 the former unique identifiers are no longer strictly
 ascending as a result of the re-ordering.

 2) If the message store has no mechanism to store unique
 identifiers, it must regenerate unique identifiers at
 each session, and each session must have a unique
 UIDVALIDITY value.




Crispin Standards Track [Page 9]

RFC 3501 IMAPv4 March 2003


 3) If the mailbox is deleted and a new mailbox with the
 same name is created at a later date, the server must
 either keep track of unique identifiers from the
 previous instance of the mailbox, or it must assign a
 new UIDVALIDITY value to the new instance of the
 mailbox. A good UIDVALIDITY value to use in this case
 is a 32-bit representation of the creation date/time of
 the mailbox. It is alright to use a constant such as
 1, but only if it guaranteed that unique identifiers
 will never be reused, even in the case of a mailbox
 being deleted (or renamed) and a new mailbox by the
 same name created at some future time.

 4) The combination of mailbox name, UIDVALIDITY, and UID
 must refer to a single immutable message on that server
 forever. In particular, the internal date, [RFC-2822]
 size, envelope, body structure, and message texts
 (RFC822, RFC822.HEADER, RFC822.TEXT, and all BODY[...]
 fetch data items) must never change. This does not
 include message numbers, nor does it include attributes
 that can be set by a STORE command (e.g., FLAGS).


2.3.1.2. Message Sequence Number Message Attribute

 A relative position from 1 to the number of messages in the mailbox.
 This position MUST be ordered by ascending unique identifier. As
 each new message is added, it is assigned a message sequence number
 that is 1 higher than the number of messages in the mailbox before
 that new message was added.

 Message sequence numbers can be reassigned during the session. For
 example, when a message is permanently removed (expunged) from the
 mailbox, the message sequence number for all subsequent messages is
 decremented. The number of messages in the mailbox is also
 decremented. Similarly, a new message can be assigned a message
 sequence number that was once held by some other message prior to an
 expunge.

 In addition to accessing messages by relative position in the
 mailbox, message sequence numbers can be used in mathematical
 calculations. For example, if an untagged "11 EXISTS" is received,
 and previously an untagged "8 EXISTS" was received, three new
 messages have arrived with message sequence numbers of 9, 10, and 11.
 Another example, if message 287 in a 523 message mailbox has UID
 12345, there are exactly 286 messages which have lesser UIDs and 236
 messages which have greater UIDs.




Crispin Standards Track [Page 10]

RFC 3501 IMAPv4 March 2003


2.3.2. Flags Message Attribute

 A list of zero or more named tokens associated with the message. A
 flag is set by its addition to this list, and is cleared by its
 removal. There are two types of flags in IMAP4rev1. A flag of
 either type can be permanent or session-only.

 A system flag is a flag name that is pre-defined in this
 specification. All system flags begin with "\". Certain system
 flags (\Deleted and \Seen) have special semantics described
 elsewhere. The currently-defined system flags are:

 \Seen
 Message has been read

 \Answered
 Message has been answered

 \Flagged
 Message is "flagged" for urgent/special attention

 \Deleted
 Message is "deleted" for removal by later EXPUNGE

 \Draft
 Message has not completed composition (marked as a draft).

 \Recent
 Message is "recently" arrived in this mailbox. This session
 is the first session to have been notified about this
 message; if the session is read-write, subsequent sessions
 will not see \Recent set for this message. This flag can not
 be altered by the client.

 If it is not possible to determine whether or not this
 session is the first session to be notified about a message,
 then that message SHOULD be considered recent.

 If multiple connections have the same mailbox selected
 simultaneously, it is undefined which of these connections
 will see newly-arrived messages with \Recent set and which
 will see it without \Recent set.

 A keyword is defined by the server implementation. Keywords do not
 begin with "\". Servers MAY permit the client to define new keywords
 in the mailbox (see the description of the PERMANENTFLAGS response
 code for more information).




Crispin Standards Track [Page 11]

RFC 3501 IMAPv4 March 2003


 A flag can be permanent or session-only on a per-flag basis.
 Permanent flags are those which the client can add or remove from the
 message flags permanently; that is, concurrent and subsequent
 sessions will see any change in permanent flags. Changes to session
 flags are valid only in that session.

 Note: The \Recent system flag is a special case of a
 session flag. \Recent can not be used as an argument in a
 STORE or APPEND command, and thus can not be changed at
 all.

2.3.3. Internal Date Message Attribute

 The internal date and time of the message on the server. This
 is not the date and time in the [RFC-2822] header, but rather a
 date and time which reflects when the message was received. In
 the case of messages delivered via [SMTP], this SHOULD be the
 date and time of final delivery of the message as defined by
 [SMTP]. In the case of messages delivered by the IMAP4rev1 COPY
 command, this SHOULD be the internal date and time of the source
 message. In the case of messages delivered by the IMAP4rev1
 APPEND command, this SHOULD be the date and time as specified in
 the APPEND command description. All other cases are
 implementation defined.

2.3.4. [RFC-2822] Size Message Attribute

 The number of octets in the message, as expressed in [RFC-2822]
 format.

2.3.5. Envelope Structure Message Attribute

 A parsed representation of the [RFC-2822] header of the message.
 Note that the IMAP Envelope structure is not the same as an
 [SMTP] envelope.

2.3.6. Body Structure Message Attribute

 A parsed representation of the [MIME-IMB] body structure
 information of the message.











Crispin Standards Track [Page 12]

RFC 3501 IMAPv4 March 2003


2.4. Message Texts

 In addition to being able to fetch the full [RFC-2822] text of a
 message, IMAP4rev1 permits the fetching of portions of the full
 message text. Specifically, it is possible to fetch the
 [RFC-2822] message header, [RFC-2822] message body, a [MIME-IMB]
 body part, or a [MIME-IMB] header.

3. State and Flow Diagram

 Once the connection between client and server is established, an
 IMAP4rev1 connection is in one of four states. The initial
 state is identified in the server greeting. Most commands are
 only valid in certain states. It is a protocol error for the
 client to attempt a command while the connection is in an
 inappropriate state, and the server will respond with a BAD or
 NO (depending upon server implementation) command completion
 result.

3.1. Not Authenticated State

 In the not authenticated state, the client MUST supply
 authentication credentials before most commands will be
 permitted. This state is entered when a connection starts
 unless the connection has been pre-authenticated.

3.2. Authenticated State

 In the authenticated state, the client is authenticated and MUST
 select a mailbox to access before commands that affect messages
 will be permitted. This state is entered when a
 pre-authenticated connection starts, when acceptable
 authentication credentials have been provided, after an error in
 selecting a mailbox, or after a successful CLOSE command.

3.3. Selected State

 In a selected state, a mailbox has been selected to access.
 This state is entered when a mailbox has been successfully
 selected.











Crispin Standards Track [Page 13]

RFC 3501 IMAPv4 March 2003


3.4. Logout State

 In the logout state, the connection is being terminated. This
 state can be entered as a result of a client request (via the
 LOGOUT command) or by unilateral action on the part of either
 the client or server.

 If the client requests the logout state, the server MUST send an
 untagged BYE response and a tagged OK response to the LOGOUT
 command before the server closes the connection; and the client
 MUST read the tagged OK response to the LOGOUT command before
 the client closes the connection.

 A server MUST NOT unilaterally close the connection without
 sending an untagged BYE response that contains the reason for
 having done so. A client SHOULD NOT unilaterally close the
 connection, and instead SHOULD issue a LOGOUT command. If the
 server detects that the client has unilaterally closed the
 connection, the server MAY omit the untagged BYE response and
 simply close its connection.































Crispin Standards Track [Page 14]

RFC 3501 IMAPv4 March 2003


 +----------------------+
 |connection established|
 +----------------------+
 ||
 \/
 +--------------------------------------+
 | server greeting |
 +--------------------------------------+
 || (1) || (2) || (3)
 \/ || ||
 +-----------------+ || ||
 |Not Authenticated| || ||
 +-----------------+ || ||
 || (7) || (4) || ||
 || \/ \/ ||
 || +----------------+ ||
 || | Authenticated |<=++ ||
 || +----------------+ || ||
 || || (7) || (5) || (6) ||
 || || \/ || ||
 || || +--------+ || ||
 || || |Selected|==++ ||
 || || +--------+ ||
 || || || (7) ||
 \/ \/ \/ \/
 +--------------------------------------+
 | Logout |
 +--------------------------------------+
 ||
 \/
 +-------------------------------+
 |both sides close the connection|
 +-------------------------------+

 (1) connection without pre-authentication (OK greeting)
 (2) pre-authenticated connection (PREAUTH greeting)
 (3) rejected connection (BYE greeting)
 (4) successful LOGIN or AUTHENTICATE command
 (5) successful SELECT or EXAMINE command
 (6) CLOSE command, or failed SELECT or EXAMINE command
 (7) LOGOUT command, server shutdown, or connection closed










Crispin Standards Track [Page 15]

RFC 3501 IMAPv4 March 2003


4. Data Formats

 IMAP4rev1 uses textual commands and responses. Data in
 IMAP4rev1 can be in one of several forms: atom, number, string,
 parenthesized list, or NIL. Note that a particular data item
 may take more than one form; for example, a data item defined as
 using "astring" syntax may be either an atom or a string.

4.1. Atom

 An atom consists of one or more non-special characters.

4.2. Number

 A number consists of one or more digit characters, and
 represents a numeric value.

4.3. String

 A string is in one of two forms: either literal or quoted
 string. The literal form is the general form of string. The
 quoted string form is an alternative that avoids the overhead of
 processing a literal at the cost of limitations of characters
 which may be used.

 A literal is a sequence of zero or more octets (including CR and
 LF), prefix-quoted with an octet count in the form of an open
 brace ("{"), the number of octets, close brace ("}"), and CRLF.
 In the case of literals transmitted from server to client, the
 CRLF is immediately followed by the octet data. In the case of
 literals transmitted from client to server, the client MUST wait
 to receive a command continuation request (described later in
 this document) before sending the octet data (and the remainder
 of the command).

 A quoted string is a sequence of zero or more 7-bit characters,
 excluding CR and LF, with double quote (<">) characters at each
 end.

 The empty string is represented as either "" (a quoted string
 with zero characters between double quotes) or as {0} followed
 by CRLF (a literal with an octet count of 0).

 Note: Even if the octet count is 0, a client transmitting a
 literal MUST wait to receive a command continuation request.






Crispin Standards Track [Page 16]

RFC 3501 IMAPv4 March 2003


4.3.1. 8-bit and Binary Strings

 8-bit textual and binary mail is supported through the use of a
 [MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY
 transmit 8-bit or multi-octet characters in literals, but SHOULD do
 so only when the [CHARSET] is identified.

 Although a BINARY body encoding is defined, unencoded binary strings
 are not permitted. A "binary string" is any string with NUL
 characters. Implementations MUST encode binary data into a textual
 form, such as BASE64, before transmitting the data. A string with an
 excessive amount of CTL characters MAY also be considered to be
 binary.

4.4. Parenthesized List

 Data structures are represented as a "parenthesized list"; a sequence
 of data items, delimited by space, and bounded at each end by
 parentheses. A parenthesized list can contain other parenthesized
 lists, using multiple levels of parentheses to indicate nesting.

 The empty list is represented as () -- a parenthesized list with no
 members.

4.5. NIL

 The special form "NIL" represents the non-existence of a particular
 data item that is represented as a string or parenthesized list, as
 distinct from the empty string "" or the empty parenthesized list ().

 Note: NIL is never used for any data item which takes the
 form of an atom. For example, a mailbox name of "NIL" is a
 mailbox named NIL as opposed to a non-existent mailbox
 name. This is because mailbox uses "astring" syntax which
 is an atom or a string. Conversely, an addr-name of NIL is
 a non-existent personal name, because addr-name uses
 "nstring" syntax which is NIL or a string, but never an
 atom.













Crispin Standards Track [Page 17]

RFC 3501 IMAPv4 March 2003


5. Operational Considerations

 The following rules are listed here to ensure that all IMAP4rev1
 implementations interoperate properly.

5.1. Mailbox Naming

 Mailbox names are 7-bit. Client implementations MUST NOT attempt to
 create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox
 names returned by LIST or LSUB as UTF-8. Server implementations
 SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT
 return 8-bit mailbox names in LIST or LSUB. See section 5.1.3 for
 more information on how to represent non-ASCII mailbox names.

 Note: 8-bit mailbox names were undefined in earlier
 versions of this protocol. Some sites used a local 8-bit
 character set to represent non-ASCII mailbox names. Such
 usage is not interoperable, and is now formally deprecated.

 The case-insensitive mailbox name INBOX is a special name reserved to
 mean "the primary mailbox for this user on this server". The
 interpretation of all other names is implementation-dependent.

 In particular, this specification takes no position on case
 sensitivity in non-INBOX mailbox names. Some server implementations
 are fully case-sensitive; others preserve case of a newly-created
 name but otherwise are case-insensitive; and yet others coerce names
 to a particular case. Client implementations MUST interact with any
 of these. If a server implementation interprets non-INBOX mailbox
 names as case-insensitive, it MUST treat names using the
 international naming convention specially as described in section
 5.1.3.

 There are certain client considerations when creating a new mailbox
 name:

 1) Any character which is one of the atom-specials (see the Formal
 Syntax) will require that the mailbox name be represented as a
 quoted string or literal.

 2) CTL and other non-graphic characters are difficult to represent
 in a user interface and are best avoided.

 3) Although the list-wildcard characters ("%" and "*") are valid
 in a mailbox name, it is difficult to use such mailbox names
 with the LIST and LSUB commands due to the conflict with
 wildcard interpretation.




Crispin Standards Track [Page 18]

RFC 3501 IMAPv4 March 2003


 4) Usually, a character (determined by the server implementation)
 is reserved to delimit levels of hierarchy.

 5) Two characters, "#" and "&", have meanings by convention, and
 should be avoided except when used in that convention.

5.1.1. Mailbox Hierarchy Naming

 If it is desired to export hierarchical mailbox names, mailbox names
 MUST be left-to-right hierarchical using a single character to
 separate levels of hierarchy. The same hierarchy separator character
 is used for all levels of hierarchy within a single name.

5.1.2. Mailbox Namespace Naming Convention

 By convention, the first hierarchical element of any mailbox name
 which begins with "#" identifies the "namespace" of the remainder of
 the name. This makes it possible to disambiguate between different
 types of mailbox stores, each of which have their own namespaces.

 For example, implementations which offer access to USENET
 newsgroups MAY use the "#news" namespace to partition the
 USENET newsgroup namespace from that of other mailboxes.
 Thus, the comp.mail.misc newsgroup would have a mailbox
 name of "#news.comp.mail.misc", and the name
 "comp.mail.misc" can refer to a different object (e.g., a
 user's private mailbox).

5.1.3. Mailbox International Naming Convention

 By convention, international mailbox names in IMAP4rev1 are specified
 using a modified version of the UTF-7 encoding described in [UTF-7].
 Modified UTF-7 may also be usable in servers that implement an
 earlier version of this protocol.

 In modified UTF-7, printable US-ASCII characters, except for "&",
 represent themselves; that is, characters with octet values 0x20-0x25
 and 0x27-0x7e. The character "&" (0x26) is represented by the
 two-octet sequence "&-".

 All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
 represented in modified BASE64, with a further modification from
 [UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be
 used to represent any printing US-ASCII character which can represent
 itself.






Crispin Standards Track [Page 19]

RFC 3501 IMAPv4 March 2003


 "&" is used to shift to modified BASE64 and "-" to shift back to
 US-ASCII. There is no implicit shift from BASE64 to US-ASCII, and
 null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII
 means "&") are not permitted. However, all names start in US-ASCII,
 and MUST end in US-ASCII; that is, a name that ends with a non-ASCII
 ISO-10646 character MUST end with a "-").

 The purpose of these modifications is to correct the following
 problems with UTF-7:

 1) UTF-7 uses the "+" character for shifting; this conflicts with
 the common use of "+" in mailbox names, in particular USENET
 newsgroup names.

 2) UTF-7's encoding is BASE64 which uses the "/" character; this
 conflicts with the use of "/" as a popular hierarchy delimiter.

 3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
 the use of "\" as a popular hierarchy delimiter.

 4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
 the use of "~" in some servers as a home directory indicator.

 5) UTF-7 permits multiple alternate forms to represent the same
 string; in particular, printable US-ASCII characters can be
 represented in encoded form.

 Although modified UTF-7 is a convention, it establishes certain
 requirements on server handling of any mailbox name with an
 embedded "&" character. In particular, server implementations
 MUST preserve the exact form of the modified BASE64 portion of a
 modified UTF-7 name and treat that text as case-sensitive, even if
 names are otherwise case-insensitive or case-folded.

 Server implementations SHOULD verify that any mailbox name with an
 embedded "&" character, used as an argument to CREATE, is: in the
 correctly modified UTF-7 syntax, has no superfluous shifts, and
 has no encoding in modified BASE64 of any printing US-ASCII
 character which can represent itself. However, client
 implementations MUST NOT depend upon the server doing this, and
 SHOULD NOT attempt to create a mailbox name with an embedded "&"
 character unless it complies with the modified UTF-7 syntax.

 Server implementations which export a mail store that does not
 follow the modified UTF-7 convention MUST convert to modified
 UTF-7 any mailbox name that contains either non-ASCII characters
 or the "&" character.




Crispin Standards Track [Page 20]

RFC 3501 IMAPv4 March 2003


 For example, here is a mailbox name which mixes English,
 Chinese, and Japanese text:
 ~peter/mail/&U,BTFw-/&ZeVnLIqe-

 For example, the string "&Jjo!" is not a valid mailbox
 name because it does not contain a shift to US-ASCII
 before the "!". The correct form is "&Jjo-!". The
 string "&U,BTFw-&ZeVnLIqe-" is not permitted because it
 contains a superfluous shift. The correct form is
 "&U,BTF2XlZyyKng-".

5.2. Mailbox Size and Message Status Updates

 At any time, a server can send data that the client did not request.
 Sometimes, such behavior is REQUIRED. For example, agents other than
 the server MAY add messages to the mailbox (e.g., new message
 delivery), change the flags of the messages in the mailbox (e.g.,
 simultaneous access to the same mailbox by multiple agents), or even
 remove messages from the mailbox. A server MUST send mailbox size
 updates automatically if a mailbox size change is observed during the
 processing of a command. A server SHOULD send message flag updates
 automatically, without requiring the client to request such updates
 explicitly.

 Special rules exist for server notification of a client about the
 removal of messages to prevent synchronization errors; see the
 description of the EXPUNGE response for more detail. In particular,
 it is NOT permitted to send an EXISTS response that would reduce the
 number of messages in the mailbox; only the EXPUNGE response can do
 this.

 Regardless of what implementation decisions a client makes on
 remembering data from the server, a client implementation MUST record
 mailbox size updates. It MUST NOT assume that any command after the
 initial mailbox selection will return the size of the mailbox.

5.3. Response when no Command in Progress

 Server implementations are permitted to send an untagged response
 (except for EXPUNGE) while there is no command in progress. Server
 implementations that send such responses MUST deal with flow control
 considerations. Specifically, they MUST either (1) verify that the
 size of the data does not exceed the underlying transport's available
 window size, or (2) use non-blocking writes.







Crispin Standards Track [Page 21]

RFC 3501 IMAPv4 March 2003


5.4. Autologout Timer

 If a server has an inactivity autologout timer, the duration of that
 timer MUST be at least 30 minutes. The receipt of ANY command from
 the client during that interval SHOULD suffice to reset the
 autologout timer.

5.5. Multiple Commands in Progress

 The client MAY send another command without waiting for the
 completion result response of a command, subject to ambiguity rules
 (see below) and flow control constraints on the underlying data
 stream. Similarly, a server MAY begin processing another command
 before processing the current command to completion, subject to
 ambiguity rules. However, any command continuation request responses
 and command continuations MUST be negotiated before any subsequent
 command is initiated.

 The exception is if an ambiguity would result because of a command
 that would affect the results of other commands. Clients MUST NOT
 send multiple commands without waiting if an ambiguity would result.
 If the server detects a possible ambiguity, it MUST execute commands
 to completion in the order given by the client.

 The most obvious example of ambiguity is when a command would affect
 the results of another command, e.g., a FETCH of a message's flags
 and a STORE of that same message's flags.

 A non-obvious ambiguity occurs with commands that permit an untagged
 EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
 since an untagged EXPUNGE response can invalidate sequence numbers in
 a subsequent command. This is not a problem for FETCH, STORE, or
 SEARCH commands because servers are prohibited from sending EXPUNGE
 responses while any of those commands are in progress. Therefore, if
 the client sends any command other than FETCH, STORE, or SEARCH, it
 MUST wait for the completion result response before sending a command
 with message sequence numbers.

 Note: UID FETCH, UID STORE, and UID SEARCH are different
 commands from FETCH, STORE, and SEARCH. If the client
 sends a UID command, it must wait for a completion result
 response before sending a command with message sequence
 numbers.








Crispin Standards Track [Page 22]

RFC 3501 IMAPv4 March 2003


 For example, the following non-waiting command sequences are invalid:

 FETCH + NOOP + STORE
 STORE + COPY + FETCH
 COPY + COPY
 CHECK + FETCH

 The following are examples of valid non-waiting command sequences:

 FETCH + STORE + SEARCH + CHECK
 STORE + COPY + EXPUNGE

 UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting
 command sequence, depending upon whether or not the second UID
 SEARCH contains message sequence numbers.

6. Client Commands

 IMAP4rev1 commands are described in this section. Commands are
 organized by the state in which the command is permitted. Commands
 which are permitted in multiple states are listed in the minimum
 permitted state (for example, commands valid in authenticated and
 selected state are listed in the authenticated state commands).

 Command arguments, identified by "Arguments:" in the command
 descriptions below, are described by function, not by syntax. The
 precise syntax of command arguments is described in the Formal Syntax
 section.

 Some commands cause specific server responses to be returned; these
 are identified by "Responses:" in the command descriptions below.
 See the response descriptions in the Responses section for
 information on these responses, and the Formal Syntax section for the
 precise syntax of these responses. It is possible for server data to
 be transmitted as a result of any command. Thus, commands that do
 not specifically require server data specify "no specific responses
 for this command" instead of "none".

 The "Result:" in the command description refers to the possible
 tagged status responses to a command, and any special interpretation
 of these status responses.

 The state of a connection is only changed by successful commands
 which are documented as changing state. A rejected command (BAD
 response) never changes the state of the connection or of the
 selected mailbox. A failed command (NO response) generally does not
 change the state of the connection or of the selected mailbox; the
 exception being the SELECT and EXAMINE commands.



Crispin Standards Track [Page 23]

RFC 3501 IMAPv4 March 2003


6.1. Client Commands - Any State

 The following commands are valid in any state: CAPABILITY, NOOP, and
 LOGOUT.

6.1.1. CAPABILITY Command

 Arguments: none

 Responses: REQUIRED untagged response: CAPABILITY

 Result: OK - capability completed
 BAD - command unknown or arguments invalid

 The CAPABILITY command requests a listing of capabilities that the
 server supports. The server MUST send a single untagged
 CAPABILITY response with "IMAP4rev1" as one of the listed
 capabilities before the (tagged) OK response.

 A capability name which begins with "AUTH=" indicates that the
 server supports that particular authentication mechanism. All
 such names are, by definition, part of this specification. For
 example, the authorization capability for an experimental
 "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not
 "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".

 Other capability names refer to extensions, revisions, or
 amendments to this specification. See the documentation of the
 CAPABILITY response for additional information. No capabilities,
 beyond the base IMAP4rev1 set defined in this specification, are
 enabled without explicit client action to invoke the capability.

 Client and server implementations MUST implement the STARTTLS,
 LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS])
 capabilities. See the Security Considerations section for
 important information.

 See the section entitled "Client Commands -
 Experimental/Expansion" for information about the form of site or
 implementation-specific capabilities.











Crispin Standards Track [Page 24]

RFC 3501 IMAPv4 March 2003


 Example: C: abcd CAPABILITY
 S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI
 LOGINDISABLED
 S: abcd OK CAPABILITY completed
 C: efgh STARTTLS
 S: efgh OK STARTLS completed
 <TLS negotiation, further commands are under [TLS] layer>
 C: ijkl CAPABILITY
 S: * CAPABILITY IMAP4rev1 AUTH=GSSAPI AUTH=PLAIN
 S: ijkl OK CAPABILITY completed


6.1.2. NOOP Command

 Arguments: none

 Responses: no specific responses for this command (but see below)

 Result: OK - noop completed
 BAD - command unknown or arguments invalid

 The NOOP command always succeeds. It does nothing.

 Since any command can return a status update as untagged data, the
 NOOP command can be used as a periodic poll for new messages or
 message status updates during a period of inactivity (this is the
 preferred method to do this). The NOOP command can also be used
 to reset any inactivity autologout timer on the server.

 Example: C: a002 NOOP
 S: a002 OK NOOP completed
 . . .
 C: a047 NOOP
 S: * 22 EXPUNGE
 S: * 23 EXISTS
 S: * 3 RECENT
 S: * 14 FETCH (FLAGS (\Seen \Deleted))
 S: a047 OK NOOP completed













Crispin Standards Track [Page 25]

RFC 3501 IMAPv4 March 2003


6.1.3. LOGOUT Command

 Arguments: none

 Responses: REQUIRED untagged response: BYE

 Result: OK - logout completed
 BAD - command unknown or arguments invalid

 The LOGOUT command informs the server that the client is done with
 the connection. The server MUST send a BYE untagged response
 before the (tagged) OK response, and then close the network
 connection.

 Example: C: A023 LOGOUT
 S: * BYE IMAP4rev1 Server logging out
 S: A023 OK LOGOUT completed
 (Server and client then close the connection)

6.2. Client Commands - Not Authenticated State

 In the not authenticated state, the AUTHENTICATE or LOGIN command
 establishes authentication and enters the authenticated state. The
 AUTHENTICATE command provides a general mechanism for a variety of
 authentication techniques, privacy protection, and integrity
 checking; whereas the LOGIN command uses a traditional user name and
 plaintext password pair and has no means of establishing privacy
 protection or integrity checking.

 The STARTTLS command is an alternate form of establishing session
 privacy protection and integrity checking, but does not establish
 authentication or enter the authenticated state.

 Server implementations MAY allow access to certain mailboxes without
 establishing authentication. This can be done by means of the
 ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older
 convention is a LOGIN command using the userid "anonymous"; in this
 case, a password is required although the server may choose to accept
 any password. The restrictions placed on anonymous users are
 implementation-dependent.

 Once authenticated (including as anonymous), it is not possible to
 re-enter not authenticated state.








Crispin Standards Track [Page 26]

RFC 3501 IMAPv4 March 2003


 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in the not authenticated state:
 STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations
 section for important information about these commands.

6.2.1. STARTTLS Command

 Arguments: none

 Responses: no specific response for this command

 Result: OK - starttls completed, begin TLS negotiation
 BAD - command unknown or arguments invalid

 A [TLS] negotiation begins immediately after the CRLF at the end
 of the tagged OK response from the server. Once a client issues a
 STARTTLS command, it MUST NOT issue further commands until a
 server response is seen and the [TLS] negotiation is complete.

 The server remains in the non-authenticated state, even if client
 credentials are supplied during the [TLS] negotiation. This does
 not preclude an authentication mechanism such as EXTERNAL (defined
 in [SASL]) from using client identity determined by the [TLS]
 negotiation.

 Once [TLS] has been started, the client MUST discard cached
 information about server capabilities and SHOULD re-issue the
 CAPABILITY command. This is necessary to protect against man-in-
 the-middle attacks which alter the capabilities list prior to
 STARTTLS. The server MAY advertise different capabilities after
 STARTTLS.

 Example: C: a001 CAPABILITY
 S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED
 S: a001 OK CAPABILITY completed
 C: a002 STARTTLS
 S: a002 OK Begin TLS negotiation now
 <TLS negotiation, further commands are under [TLS] layer>
 C: a003 CAPABILITY
 S: * CAPABILITY IMAP4rev1 AUTH=PLAIN
 S: a003 OK CAPABILITY completed
 C: a004 LOGIN joe password
 S: a004 OK LOGIN completed








Crispin Standards Track [Page 27]

RFC 3501 IMAPv4 March 2003


6.2.2. AUTHENTICATE Command

 Arguments: authentication mechanism name

 Responses: continuation data can be requested

 Result: OK - authenticate completed, now in authenticated state
 NO - authenticate failure: unsupported authentication
 mechanism, credentials rejected
 BAD - command unknown or arguments invalid,
 authentication exchange cancelled

 The AUTHENTICATE command indicates a [SASL] authentication
 mechanism to the server. If the server supports the requested
 authentication mechanism, it performs an authentication protocol
 exchange to authenticate and identify the client. It MAY also
 negotiate an OPTIONAL security layer for subsequent protocol
 interactions. If the requested authentication mechanism is not
 supported, the server SHOULD reject the AUTHENTICATE command by
 sending a tagged NO response.

 The AUTHENTICATE command does not support the optional "initial
 response" feature of [SASL]. Section 5.1 of [SASL] specifies how
 to handle an authentication mechanism which uses an initial
 response.

 The service name specified by this protocol's profile of [SASL] is
 "imap".

 The authentication protocol exchange consists of a series of
 server challenges and client responses that are specific to the
 authentication mechanism. A server challenge consists of a
 command continuation request response with the "+" token followed
 by a BASE64 encoded string. The client response consists of a
 single line consisting of a BASE64 encoded string. If the client
 wishes to cancel an authentication exchange, it issues a line
 consisting of a single "*". If the server receives such a
 response, it MUST reject the AUTHENTICATE command by sending a
 tagged BAD response.

 If a security layer is negotiated through the [SASL]
 authentication exchange, it takes effect immediately following the
 CRLF that concludes the authentication exchange for the client,
 and the CRLF of the tagged OK response for the server.

 While client and server implementations MUST implement the
 AUTHENTICATE command itself, it is not required to implement any
 authentication mechanisms other than the PLAIN mechanism described



Crispin Standards Track [Page 28]

RFC 3501 IMAPv4 March 2003


 in [IMAP-TLS]. Also, an authentication mechanism is not required
 to support any security layers.

 Note: a server implementation MUST implement a
 configuration in which it does NOT permit any plaintext
 password mechanisms, unless either the STARTTLS command
 has been negotiated or some other mechanism that
 protects the session from password snooping has been
 provided. Server sites SHOULD NOT use any configuration
 which permits a plaintext password mechanism without
 such a protection mechanism against password snooping.
 Client and server implementations SHOULD implement
 additional [SASL] mechanisms that do not use plaintext
 passwords, such the GSSAPI mechanism described in [SASL]
 and/or the [DIGEST-MD5] mechanism.

 Servers and clients can support multiple authentication
 mechanisms. The server SHOULD list its supported authentication
 mechanisms in the response to the CAPABILITY command so that the
 client knows which authentication mechanisms to use.

 A server MAY include a CAPABILITY response code in the tagged OK
 response of a successful AUTHENTICATE command in order to send
 capabilities automatically. It is unnecessary for a client to
 send a separate CAPABILITY command if it recognizes these
 automatic capabilities. This should only be done if a security
 layer was not negotiated by the AUTHENTICATE command, because the
 tagged OK response as part of an AUTHENTICATE command is not
 protected by encryption/integrity checking. [SASL] requires the
 client to re-issue a CAPABILITY command in this case.

 If an AUTHENTICATE command fails with a NO response, the client
 MAY try another authentication mechanism by issuing another
 AUTHENTICATE command. It MAY also attempt to authenticate by
 using the LOGIN command (see section 6.2.3 for more detail). In
 other words, the client MAY request authentication types in
 decreasing order of preference, with the LOGIN command as a last
 resort.

 The authorization identity passed from the client to the server
 during the authentication exchange is interpreted by the server as
 the user name whose privileges the client is requesting.









Crispin Standards Track [Page 29]

RFC 3501 IMAPv4 March 2003


 Example: S: * OK IMAP4rev1 Server
 C: A001 AUTHENTICATE GSSAPI
 S: +
 C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw
 MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0
 b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW
 Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA
 cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX
 AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y
 C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb
 I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi
 vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL
 pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n
 FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE
 NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx
 O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB
 vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg==
 S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC
 AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0
 uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg==
 C:
 S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe
 ceP2CWY0SR0fAQAgAAQEBAQ=
 C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP
 wkhbfa2QteAQAgAG1yYwE=
 S: A001 OK GSSAPI authentication successful

 Note: The line breaks within server challenges and client
 responses are for editorial clarity and are not in real
 authenticators.


6.2.3. LOGIN Command

 Arguments: user name
 password

 Responses: no specific responses for this command

 Result: OK - login completed, now in authenticated state
 NO - login failure: user name or password rejected
 BAD - command unknown or arguments invalid

 The LOGIN command identifies the client to the server and carries
 the plaintext password authenticating this user.






Crispin Standards Track [Page 30]

RFC 3501 IMAPv4 March 2003


 A server MAY include a CAPABILITY response code in the tagged OK
 response to a successful LOGIN command in order to send
 capabilities automatically. It is unnecessary for a client to
 send a separate CAPABILITY command if it recognizes these
 automatic capabilities.

 Example: C: a001 LOGIN SMITH SESAME
 S: a001 OK LOGIN completed

 Note: Use of the LOGIN command over an insecure network
 (such as the Internet) is a security risk, because anyone
 monitoring network traffic can obtain plaintext passwords.
 The LOGIN command SHOULD NOT be used except as a last
 resort, and it is recommended that client implementations
 have a means to disable any automatic use of the LOGIN
 command.

 Unless either the STARTTLS command has been negotiated or
 some other mechanism that protects the session from
 password snooping has been provided, a server
 implementation MUST implement a configuration in which it
 advertises the LOGINDISABLED capability and does NOT permit
 the LOGIN command. Server sites SHOULD NOT use any
 configuration which permits the LOGIN command without such
 a protection mechanism against password snooping. A client
 implementation MUST NOT send a LOGIN command if the
 LOGINDISABLED capability is advertised.

6.3. Client Commands - Authenticated State

 In the authenticated state, commands that manipulate mailboxes as
 atomic entities are permitted. Of these commands, the SELECT and
 EXAMINE commands will select a mailbox for access and enter the
 selected state.

 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in the authenticated state: SELECT,
 EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
 STATUS, and APPEND.












Crispin Standards Track [Page 31]

RFC 3501 IMAPv4 March 2003


6.3.1. SELECT Command

 Arguments: mailbox name

 Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
 REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS,
 UIDNEXT, UIDVALIDITY

 Result: OK - select completed, now in selected state
 NO - select failure, now in authenticated state: no
 such mailbox, can't access mailbox
 BAD - command unknown or arguments invalid

 The SELECT command selects a mailbox so that messages in the
 mailbox can be accessed. Before returning an OK to the client,
 the server MUST send the following untagged data to the client.
 Note that earlier versions of this protocol only required the
 FLAGS, EXISTS, and RECENT untagged data; consequently, client
 implementations SHOULD implement default behavior for missing data
 as discussed with the individual item.

 FLAGS Defined flags in the mailbox. See the description
 of the FLAGS response for more detail.

 <n> EXISTS The number of messages in the mailbox. See the
 description of the EXISTS response for more detail.

 <n> RECENT The number of messages with the \Recent flag set.
 See the description of the RECENT response for more
 detail.

 OK [UNSEEN <n>]
 The message sequence number of the first unseen
 message in the mailbox. If this is missing, the
 client can not make any assumptions about the first
 unseen message in the mailbox, and needs to issue a
 SEARCH command if it wants to find it.

 OK [PERMANENTFLAGS (<list of flags>)]
 A list of message flags that the client can change
 permanently. If this is missing, the client should
 assume that all flags can be changed permanently.

 OK [UIDNEXT <n>]
 The next unique identifier value. Refer to section
 2.3.1.1 for more information. If this is missing,
 the client can not make any assumptions about the
 next unique identifier value.



Crispin Standards Track [Page 32]

RFC 3501 IMAPv4 March 2003


 OK [UIDVALIDITY <n>]
 The unique identifier validity value. Refer to
 section 2.3.1.1 for more information. If this is
 missing, the server does not support unique
 identifiers.

 Only one mailbox can be selected at a time in a connection;
 simultaneous access to multiple mailboxes requires multiple
 connections. The SELECT command automatically deselects any
 currently selected mailbox before attempting the new selection.
 Consequently, if a mailbox is selected and a SELECT command that
 fails is attempted, no mailbox is selected.

 If the client is permitted to modify the mailbox, the server
 SHOULD prefix the text of the tagged OK response with the
 "[READ-WRITE]" response code.

 If the client is not permitted to modify the mailbox but is
 permitted read access, the mailbox is selected as read-only, and
 the server MUST prefix the text of the tagged OK response to
 SELECT with the "[READ-ONLY]" response code. Read-only access
 through SELECT differs from the EXAMINE command in that certain
 read-only mailboxes MAY permit the change of permanent state on a
 per-user (as opposed to global) basis. Netnews messages marked in
 a server-based .newsrc file are an example of such per-user
 permanent state that can be modified with read-only mailboxes.

 Example: C: A142 SELECT INBOX
 S: * 172 EXISTS
 S: * 1 RECENT
 S: * OK [UNSEEN 12] Message 12 is first unseen
 S: * OK [UIDVALIDITY 3857529045] UIDs valid
 S: * OK [UIDNEXT 4392] Predicted next UID
 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
 S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
 S: A142 OK [READ-WRITE] SELECT completed















Crispin Standards Track [Page 33]

RFC 3501 IMAPv4 March 2003


6.3.2. EXAMINE Command

 Arguments: mailbox name

 Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
 REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS,
 UIDNEXT, UIDVALIDITY

 Result: OK - examine completed, now in selected state
 NO - examine failure, now in authenticated state: no
 such mailbox, can't access mailbox
 BAD - command unknown or arguments invalid

 The EXAMINE command is identical to SELECT and returns the same
 output; however, the selected mailbox is identified as read-only.
 No changes to the permanent state of the mailbox, including
 per-user state, are permitted; in particular, EXAMINE MUST NOT
 cause messages to lose the \Recent flag.

 The text of the tagged OK response to the EXAMINE command MUST
 begin with the "[READ-ONLY]" response code.

 Example: C: A932 EXAMINE blurdybloop
 S: * 17 EXISTS
 S: * 2 RECENT
 S: * OK [UNSEEN 8] Message 8 is first unseen
 S: * OK [UIDVALIDITY 3857529045] UIDs valid
 S: * OK [UIDNEXT 4392] Predicted next UID
 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
 S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
 S: A932 OK [READ-ONLY] EXAMINE completed


6.3.3. CREATE Command

 Arguments: mailbox name

 Responses: no specific responses for this command

 Result: OK - create completed
 NO - create failure: can't create mailbox with that name
 BAD - command unknown or arguments invalid

 The CREATE command creates a mailbox with the given name. An OK
 response is returned only if a new mailbox with that name has been
 created. It is an error to attempt to create INBOX or a mailbox
 with a name that refers to an extant mailbox. Any error in
 creation will return a tagged NO response.



Crispin Standards Track [Page 34]

RFC 3501 IMAPv4 March 2003


 If the mailbox name is suffixed with the server's hierarchy
 separator character (as returned from the server by a LIST
 command), this is a declaration that the client intends to create
 mailbox names under this name in the hierarchy. Server
 implementations that do not require this declaration MUST ignore
 the declaration. In any case, the name created is without the
 trailing hierarchy delimiter.

 If the server's hierarchy separator character appears elsewhere in
 the name, the server SHOULD create any superior hierarchical names
 that are needed for the CREATE command to be successfully
 completed. In other words, an attempt to create "foo/bar/zap" on
 a server in which "/" is the hierarchy separator character SHOULD
 create foo/ and foo/bar/ if they do not already exist.

 If a new mailbox is created with the same name as a mailbox which
 was deleted, its unique identifiers MUST be greater than any
 unique identifiers used in the previous incarnation of the mailbox
 UNLESS the new incarnation has a different unique identifier
 validity value. See the description of the UID command for more
 detail.

 Example: C: A003 CREATE owatagusiam/
 S: A003 OK CREATE completed
 C: A004 CREATE owatagusiam/blurdybloop
 S: A004 OK CREATE completed

 Note: The interpretation of this example depends on whether
 "/" was returned as the hierarchy separator from LIST. If
 "/" is the hierarchy separator, a new level of hierarchy
 named "owatagusiam" with a member called "blurdybloop" is
 created. Otherwise, two mailboxes at the same hierarchy
 level are created.


6.3.4. DELETE Command

 Arguments: mailbox name

 Responses: no specific responses for this command

 Result: OK - delete completed
 NO - delete failure: can't delete mailbox with that name
 BAD - command unknown or arguments invalid







Crispin Standards Track [Page 35]

RFC 3501 IMAPv4 March 2003


 The DELETE command permanently removes the mailbox with the given
 name. A tagged OK response is returned only if the mailbox has
 been deleted. It is an error to attempt to delete INBOX or a
 mailbox name that does not exist.

 The DELETE command MUST NOT remove inferior hierarchical names.
 For example, if a mailbox "foo" has an inferior "foo.bar"
 (assuming "." is the hierarchy delimiter character), removing
 "foo" MUST NOT remove "foo.bar". It is an error to attempt to
 delete a name that has inferior hierarchical names and also has
 the \Noselect mailbox name attribute (see the description of the
 LIST response for more details).

 It is permitted to delete a name that has inferior hierarchical
 names and does not have the \Noselect mailbox name attribute. In
 this case, all messages in that mailbox are removed, and the name
 will acquire the \Noselect mailbox name attribute.

 The value of the highest-used unique identifier of the deleted
 mailbox MUST be preserved so that a new mailbox created with the
 same name will not reuse the identifiers of the former
 incarnation, UNLESS the new incarnation has a different unique
 identifier validity value. See the description of the UID command
 for more detail.

 Examples: C: A682 LIST "" *
 S: * LIST () "/" blurdybloop
 S: * LIST (\Noselect) "/" foo
 S: * LIST () "/" foo/bar
 S: A682 OK LIST completed
 C: A683 DELETE blurdybloop
 S: A683 OK DELETE completed
 C: A684 DELETE foo
 S: A684 NO Name "foo" has inferior hierarchical names
 C: A685 DELETE foo/bar
 S: A685 OK DELETE Completed
 C: A686 LIST "" *
 S: * LIST (\Noselect) "/" foo
 S: A686 OK LIST completed
 C: A687 DELETE foo
 S: A687 OK DELETE Completed










Crispin Standards Track [Page 36]

RFC 3501 IMAPv4 March 2003


 C: A82 LIST "" *
 S: * LIST () "." blurdybloop
 S: * LIST () "." foo
 S: * LIST () "." foo.bar
 S: A82 OK LIST completed
 C: A83 DELETE blurdybloop
 S: A83 OK DELETE completed
 C: A84 DELETE foo
 S: A84 OK DELETE Completed
 C: A85 LIST "" *
 S: * LIST () "." foo.bar
 S: A85 OK LIST completed
 C: A86 LIST "" %
 S: * LIST (\Noselect) "." foo
 S: A86 OK LIST completed


6.3.5. RENAME Command

 Arguments: existing mailbox name
 new mailbox name

 Responses: no specific responses for this command

 Result: OK - rename completed
 NO - rename failure: can't rename mailbox with that name,
 can't rename to mailbox with that name
 BAD - command unknown or arguments invalid

 The RENAME command changes the name of a mailbox. A tagged OK
 response is returned only if the mailbox has been renamed. It is
 an error to attempt to rename from a mailbox name that does not
 exist or to a mailbox name that already exists. Any error in
 renaming will return a tagged NO response.

 If the name has inferior hierarchical names, then the inferior
 hierarchical names MUST also be renamed. For example, a rename of
 "foo" to "zap" will rename "foo/bar" (assuming "/" is the
 hierarchy delimiter character) to "zap/bar".

 If the server's hierarchy separator character appears in the name,
 the server SHOULD create any superior hierarchical names that are
 needed for the RENAME command to complete successfully. In other
 words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a
 server in which "/" is the hierarchy separator character SHOULD
 create baz/ and baz/rag/ if they do not already exist.





Crispin Standards Track [Page 37]

RFC 3501 IMAPv4 March 2003


 The value of the highest-used unique identifier of the old mailbox
 name MUST be preserved so that a new mailbox created with the same
 name will not reuse the identifiers of the former incarnation,
 UNLESS the new incarnation has a different unique identifier
 validity value. See the description of the UID command for more
 detail.

 Renaming INBOX is permitted, and has special behavior. It moves
 all messages in INBOX to a new mailbox with the given name,
 leaving INBOX empty. If the server implementation supports
 inferior hierarchical names of INBOX, these are unaffected by a
 rename of INBOX.

 Examples: C: A682 LIST "" *
 S: * LIST () "/" blurdybloop
 S: * LIST (\Noselect) "/" foo
 S: * LIST () "/" foo/bar
 S: A682 OK LIST completed
 C: A683 RENAME blurdybloop sarasoop
 S: A683 OK RENAME completed
 C: A684 RENAME foo zowie
 S: A684 OK RENAME Completed
 C: A685 LIST "" *
 S: * LIST () "/" sarasoop
 S: * LIST (\Noselect) "/" zowie
 S: * LIST () "/" zowie/bar
 S: A685 OK LIST completed

 C: Z432 LIST "" *
 S: * LIST () "." INBOX
 S: * LIST () "." INBOX.bar
 S: Z432 OK LIST completed
 C: Z433 RENAME INBOX old-mail
 S: Z433 OK RENAME completed
 C: Z434 LIST "" *
 S: * LIST () "." INBOX
 S: * LIST () "." INBOX.bar
 S: * LIST () "." old-mail
 S: Z434 OK LIST completed












Crispin Standards Track [Page 38]

RFC 3501 IMAPv4 March 2003


6.3.6. SUBSCRIBE Command

 Arguments: mailbox

 Responses: no specific responses for this command

 Result: OK - subscribe completed
 NO - subscribe failure: can't subscribe to that name
 BAD - command unknown or arguments invalid

 The SUBSCRIBE command adds the specified mailbox name to the
 server's set of "active" or "subscribed" mailboxes as returned by
 the LSUB command. This command returns a tagged OK response only
 if the subscription is successful.

 A server MAY validate the mailbox argument to SUBSCRIBE to verify
 that it exists. However, it MUST NOT unilaterally remove an
 existing mailbox name from the subscription list even if a mailbox
 by that name no longer exists.

 Note: This requirement is because a server site can
 choose to routinely remove a mailbox with a well-known
 name (e.g., "system-alerts") after its contents expire,
 with the intention of recreating it when new contents
 are appropriate.


 Example: C: A002 SUBSCRIBE #news.comp.mail.mime
 S: A002 OK SUBSCRIBE completed


6.3.7. UNSUBSCRIBE Command

 Arguments: mailbox name

 Responses: no specific responses for this command

 Result: OK - unsubscribe completed
 NO - unsubscribe failure: can't unsubscribe that name
 BAD - command unknown or arguments invalid

 The UNSUBSCRIBE command removes the specified mailbox name from
 the server's set of "active" or "subscribed" mailboxes as returned
 by the LSUB command. This command returns a tagged OK response
 only if the unsubscription is successful.

 Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime
 S: A002 OK UNSUBSCRIBE completed



Crispin Standards Track [Page 39]

RFC 3501 IMAPv4 March 2003


6.3.8. LIST Command

 Arguments: reference name
 mailbox name with possible wildcards

 Responses: untagged responses: LIST

 Result: OK - list completed
 NO - list failure: can't list that reference or name
 BAD - command unknown or arguments invalid

 The LIST command returns a subset of names from the complete set
 of all names available to the client. Zero or more untagged LIST
 replies are returned, containing the name attributes, hierarchy
 delimiter, and name; see the description of the LIST reply for
 more detail.

 The LIST command SHOULD return its data quickly, without undue
 delay. For example, it SHOULD NOT go to excess trouble to
 calculate the \Marked or \Unmarked status or perform other
 processing; if each name requires 1 second of processing, then a
 list of 1200 names would take 20 minutes!

 An empty ("" string) reference name argument indicates that the
 mailbox name is interpreted as by SELECT. The returned mailbox
 names MUST match the supplied mailbox name pattern. A non-empty
 reference name argument is the name of a mailbox or a level of
 mailbox hierarchy, and indicates the context in which the mailbox
 name is interpreted.

 An empty ("" string) mailbox name argument is a special request to
 return the hierarchy delimiter and the root name of the name given
 in the reference. The value returned as the root MAY be the empty
 string if the reference is non-rooted or is an empty string. In
 all cases, a hierarchy delimiter (or NIL if there is no hierarchy)
 is returned. This permits a client to get the hierarchy delimiter
 (or find out that the mailbox names are flat) even when no
 mailboxes by that name currently exist.

 The reference and mailbox name arguments are interpreted into a
 canonical form that represents an unambiguous left-to-right
 hierarchy. The returned mailbox names will be in the interpreted
 form.








Crispin Standards Track [Page 40]

RFC 3501 IMAPv4 March 2003


 Note: The interpretation of the reference argument is
 implementation-defined. It depends upon whether the
 server implementation has a concept of the "current
 working directory" and leading "break out characters",
 which override the current working directory.

 For example, on a server which exports a UNIX or NT
 filesystem, the reference argument contains the current
 working directory, and the mailbox name argument would
 contain the name as interpreted in the current working
 directory.

 If a server implementation has no concept of break out
 characters, the canonical form is normally the reference
 name appended with the mailbox name. Note that if the
 server implements the namespace convention (section
 5.1.2), "#" is a break out character and must be treated
 as such.

 If the reference argument is not a level of mailbox
 hierarchy (that is, it is a \NoInferiors name), and/or
 the reference argument does not end with the hierarchy
 delimiter, it is implementation-dependent how this is
 interpreted. For example, a reference of "foo/bar" and
 mailbox name of "rag/baz" could be interpreted as
 "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/baz".
 A client SHOULD NOT use such a reference argument except
 at the explicit request of the user. A hierarchical
 browser MUST NOT make any assumptions about server
 interpretation of the reference unless the reference is
 a level of mailbox hierarchy AND ends with the hierarchy
 delimiter.

 Any part of the reference argument that is included in the
 interpreted form SHOULD prefix the interpreted form. It SHOULD
 also be in the same form as the reference name argument. This
 rule permits the client to determine if the returned mailbox name
 is in the context of the reference argument, or if something about
 the mailbox argument overrode the reference argument. Without
 this rule, the client would have to have knowledge of the server's
 naming semantics including what characters are "breakouts" that
 override a naming context.









Crispin Standards Track [Page 41]

RFC 3501 IMAPv4 March 2003


 For example, here are some examples of how references
 and mailbox names might be interpreted on a UNIX-based
 server:

 Reference Mailbox Name Interpretation
 ------------ ------------ --------------
 ~smith/Mail/ foo.* ~smith/Mail/foo.*
 archive/ % archive/%
 #news. comp.mail.* #news.comp.mail.*
 ~smith/Mail/ /usr/doc/foo /usr/doc/foo
 archive/ ~fred/Mail/* ~fred/Mail/*

 The first three examples demonstrate interpretations in
 the context of the reference argument. Note that
 "~smith/Mail" SHOULD NOT be transformed into something
 like "/u2/users/smith/Mail", or it would be impossible
 for the client to determine that the interpretation was
 in the context of the reference.

 The character "*" is a wildcard, and matches zero or more
 characters at this position. The character "%" is similar to "*",
 but it does not match a hierarchy delimiter. If the "%" wildcard
 is the last character of a mailbox name argument, matching levels
 of hierarchy are also returned. If these levels of hierarchy are
 not also selectable mailboxes, they are returned with the
 \Noselect mailbox name attribute (see the description of the LIST
 response for more details).

 Server implementations are permitted to "hide" otherwise
 accessible mailboxes from the wildcard characters, by preventing
 certain characters or names from matching a wildcard in certain
 situations. For example, a UNIX-based server might restrict the
 interpretation of "*" so that an initial "/" character does not
 match.

 The special name INBOX is included in the output from LIST, if
 INBOX is supported by this server for this user and if the
 uppercase string "INBOX" matches the interpreted reference and
 mailbox name arguments with wildcards as described above. The
 criteria for omitting INBOX is whether SELECT INBOX will return
 failure; it is not relevant whether the user's real INBOX resides
 on this or some other server.









Crispin Standards Track [Page 42]

RFC 3501 IMAPv4 March 2003


 Example: C: A101 LIST "" ""
 S: * LIST (\Noselect) "/" ""
 S: A101 OK LIST Completed
 C: A102 LIST #news.comp.mail.misc ""
 S: * LIST (\Noselect) "." #news.
 S: A102 OK LIST Completed
 C: A103 LIST /usr/staff/jones ""
 S: * LIST (\Noselect) "/" /
 S: A103 OK LIST Completed
 C: A202 LIST ~/Mail/ %
 S: * LIST (\Noselect) "/" ~/Mail/foo
 S: * LIST () "/" ~/Mail/meetings
 S: A202 OK LIST completed


6.3.9. LSUB Command

 Arguments: reference name
 mailbox name with possible wildcards

 Responses: untagged responses: LSUB

 Result: OK - lsub completed
 NO - lsub failure: can't list that reference or name
 BAD - command unknown or arguments invalid

 The LSUB command returns a subset of names from the set of names
 that the user has declared as being "active" or "subscribed".
 Zero or more untagged LSUB replies are returned. The arguments to
 LSUB are in the same form as those for LIST.

 The returned untagged LSUB response MAY contain different mailbox
 flags from a LIST untagged response. If this should happen, the
 flags in the untagged LIST are considered more authoritative.

 A special situation occurs when using LSUB with the % wildcard.
 Consider what happens if "foo/bar" (with a hierarchy delimiter of
 "/") is subscribed but "foo" is not. A "%" wildcard to LSUB must
 return foo, not foo/bar, in the LSUB response, and it MUST be
 flagged with the \Noselect attribute.

 The server MUST NOT unilaterally remove an existing mailbox name
 from the subscription list even if a mailbox by that name no
 longer exists.







Crispin Standards Track [Page 43]

RFC 3501 IMAPv4 March 2003


 Example: C: A002 LSUB "#news." "comp.mail.*"
 S: * LSUB () "." #news.comp.mail.mime
 S: * LSUB () "." #news.comp.mail.misc
 S: A002 OK LSUB completed
 C: A003 LSUB "#news." "comp.%"
 S: * LSUB (\NoSelect) "." #news.comp.mail
 S: A003 OK LSUB completed


6.3.10. STATUS Command

 Arguments: mailbox name
 status data item names

 Responses: untagged responses: STATUS

 Result: OK - status completed
 NO - status failure: no status for that name
 BAD - command unknown or arguments invalid

 The STATUS command requests the status of the indicated mailbox.
 It does not change the currently selected mailbox, nor does it
 affect the state of any messages in the queried mailbox (in
 particular, STATUS MUST NOT cause messages to lose the \Recent
 flag).

 The STATUS command provides an alternative to opening a second
 IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
 query that mailbox's status without deselecting the current
 mailbox in the first IMAP4rev1 connection.

 Unlike the LIST command, the STATUS command is not guaranteed to
 be fast in its response. Under certain circumstances, it can be
 quite slow. In some implementations, the server is obliged to
 open the mailbox read-only internally to obtain certain status
 information. Also unlike the LIST command, the STATUS command
 does not accept wildcards.

 Note: The STATUS command is intended to access the
 status of mailboxes other than the currently selected
 mailbox. Because the STATUS command can cause the
 mailbox to be opened internally, and because this
 information is available by other means on the selected
 mailbox, the STATUS command SHOULD NOT be used on the
 currently selected mailbox.






Crispin Standards Track [Page 44]

RFC 3501 IMAPv4 March 2003


 The STATUS command MUST NOT be used as a "check for new
 messages in the selected mailbox" operation (refer to
 sections 7, 7.3.1, and 7.3.2 for more information about
 the proper method for new message checking).

 Because the STATUS command is not guaranteed to be fast
 in its results, clients SHOULD NOT expect to be able to
 issue many consecutive STATUS commands and obtain
 reasonable performance.

 The currently defined status data items that can be requested are:

 MESSAGES
 The number of messages in the mailbox.

 RECENT
 The number of messages with the \Recent flag set.

 UIDNEXT
 The next unique identifier value of the mailbox. Refer to
 section 2.3.1.1 for more information.

 UIDVALIDITY
 The unique identifier validity value of the mailbox. Refer to
 section 2.3.1.1 for more information.

 UNSEEN
 The number of messages which do not have the \Seen flag set.


 Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
 S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
 S: A042 OK STATUS completed


















Crispin Standards Track [Page 45]

RFC 3501 IMAPv4 March 2003


6.3.11. APPEND Command

 Arguments: mailbox name
 OPTIONAL flag parenthesized list
 OPTIONAL date/time string
 message literal

 Responses: no specific responses for this command

 Result: OK - append completed
 NO - append error: can't append to that mailbox, error
 in flags or date/time or message text
 BAD - command unknown or arguments invalid

 The APPEND command appends the literal argument as a new message
 to the end of the specified destination mailbox. This argument
 SHOULD be in the format of an [RFC-2822] message. 8-bit
 characters are permitted in the message. A server implementation
 that is unable to preserve 8-bit data properly MUST be able to
 reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB]
 content transfer encoding.

 Note: There MAY be exceptions, e.g., draft messages, in
 which required [RFC-2822] header lines are omitted in
 the message literal argument to APPEND. The full
 implications of doing so MUST be understood and
 carefully weighed.

 If a flag parenthesized list is specified, the flags SHOULD be set
 in the resulting message; otherwise, the flag list of the
 resulting message is set to empty by default. In either case, the
 Recent flag is also set.

 If a date-time is specified, the internal date SHOULD be set in
 the resulting message; otherwise, the internal date of the
 resulting message is set to the current date and time by default.

 If the append is unsuccessful for any reason, the mailbox MUST be
 restored to its state before the APPEND attempt; no partial
 appending is permitted.

 If the destination mailbox does not exist, a server MUST return an
 error, and MUST NOT automatically create the mailbox. Unless it
 is certain that the destination mailbox can not be created, the
 server MUST send the response code "[TRYCREATE]" as the prefix of
 the text of the tagged NO response. This gives a hint to the
 client that it can attempt a CREATE command and retry the APPEND
 if the CREATE is successful.



Crispin Standards Track [Page 46]

RFC 3501 IMAPv4 March 2003


 If the mailbox is currently selected, the normal new message
 actions SHOULD occur. Specifically, the server SHOULD notify the
 client immediately via an untagged EXISTS response. If the server
 does not do so, the client MAY issue a NOOP command (or failing
 that, a CHECK command) after one or more APPEND commands.

 Example: C: A003 APPEND saved-messages (\Seen) {310}
 S: + Ready for literal data
 C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
 C: From: Fred Foobar <foobar@Blurdybloop.COM>
 C: Subject: afternoon meeting
 C: To: mooch@owatagu.siam.edu
 C: Message-Id: <B27397-0100000@Blurdybloop.COM>
 C: MIME-Version: 1.0
 C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
 C:
 C: Hello Joe, do you think we can meet at 3:30 tomorrow?
 C:
 S: A003 OK APPEND completed

 Note: The APPEND command is not used for message delivery,
 because it does not provide a mechanism to transfer [SMTP]
 envelope information.

6.4. Client Commands - Selected State

 In the selected state, commands that manipulate messages in a mailbox
 are permitted.

 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 and the authenticated state commands (SELECT, EXAMINE, CREATE,
 DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and
 APPEND), the following commands are valid in the selected state:
 CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID.

6.4.1. CHECK Command

 Arguments: none

 Responses: no specific responses for this command

 Result: OK - check completed
 BAD - command unknown or arguments invalid

 The CHECK command requests a checkpoint of the currently selected
 mailbox. A checkpoint refers to any implementation-dependent
 housekeeping associated with the mailbox (e.g., resolving the
 server's in-memory state of the mailbox with the state on its



Crispin Standards Track [Page 47]

RFC 3501 IMAPv4 March 2003


 disk) that is not normally executed as part of each command. A
 checkpoint MAY take a non-instantaneous amount of real time to
 complete. If a server implementation has no such housekeeping
 considerations, CHECK is equivalent to NOOP.

 There is no guarantee that an EXISTS untagged response will happen
 as a result of CHECK. NOOP, not CHECK, SHOULD be used for new
 message polling.

 Example: C: FXXZ CHECK
 S: FXXZ OK CHECK Completed


6.4.2. CLOSE Command

 Arguments: none

 Responses: no specific responses for this command

 Result: OK - close completed, now in authenticated state
 BAD - command unknown or arguments invalid

 The CLOSE command permanently removes all messages that have the
 \Deleted flag set from the currently selected mailbox, and returns
 to the authenticated state from the selected state. No untagged
 EXPUNGE responses are sent.

 No messages are removed, and no error is given, if the mailbox is
 selected by an EXAMINE command or is otherwise selected read-only.

 Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT
 command MAY be issued without previously issuing a CLOSE command.
 The SELECT, EXAMINE, and LOGOUT commands implicitly close the
 currently selected mailbox without doing an expunge. However,
 when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT
 sequence is considerably faster than an EXPUNGE-LOGOUT or
 EXPUNGE-SELECT because no untagged EXPUNGE responses (which the
 client would probably ignore) are sent.

 Example: C: A341 CLOSE
 S: A341 OK CLOSE completed










Crispin Standards Track [Page 48]

RFC 3501 IMAPv4 March 2003


6.4.3. EXPUNGE Command

 Arguments: none

 Responses: untagged responses: EXPUNGE

 Result: OK - expunge completed
 NO - expunge failure: can't expunge (e.g., permission
 denied)
 BAD - command unknown or arguments invalid

 The EXPUNGE command permanently removes all messages that have the
 \Deleted flag set from the currently selected mailbox. Before
 returning an OK to the client, an untagged EXPUNGE response is
 sent for each message that is removed.

 Example: C: A202 EXPUNGE
 S: * 3 EXPUNGE
 S: * 3 EXPUNGE
 S: * 5 EXPUNGE
 S: * 8 EXPUNGE
 S: A202 OK EXPUNGE completed

 Note: In this example, messages 3, 4, 7, and 11 had the
 \Deleted flag set. See the description of the EXPUNGE
 response for further explanation.


6.4.4. SEARCH Command

 Arguments: OPTIONAL [CHARSET] specification
 searching criteria (one or more)

 Responses: REQUIRED untagged response: SEARCH

 Result: OK - search completed
 NO - search error: can't search that [CHARSET] or
 criteria
 BAD - command unknown or arguments invalid

 The SEARCH command searches the mailbox for messages that match
 the given searching criteria. Searching criteria consist of one
 or more search keys. The untagged SEARCH response from the server
 contains a listing of message sequence numbers corresponding to
 those messages that match the searching criteria.






Crispin Standards Track [Page 49]

RFC 3501 IMAPv4 March 2003


 When multiple keys are specified, the result is the intersection
 (AND function) of all the messages that match those keys. For
 example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers
 to all deleted messages from Smith that were placed in the mailbox
 since February 1, 1994. A search key can also be a parenthesized
 list of one or more search keys (e.g., for use with the OR and NOT
 keys).

 Server implementations MAY exclude [MIME-IMB] body parts with
 terminal content media types other than TEXT and MESSAGE from
 consideration in SEARCH matching.

 The OPTIONAL [CHARSET] specification consists of the word
 "CHARSET" followed by a registered [CHARSET]. It indicates the
 [CHARSET] of the strings that appear in the search criteria.
 [MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in
 [RFC-2822]/[MIME-IMB] headers, MUST be decoded before comparing
 text in a [CHARSET] other than US-ASCII. US-ASCII MUST be
 supported; other [CHARSET]s MAY be supported.

 If the server does not support the specified [CHARSET], it MUST
 return a tagged NO response (not a BAD). This response SHOULD
 contain the BADCHARSET response code, which MAY list the
 [CHARSET]s supported by the server.

 In all search keys that use strings, a message matches the key if
 the string is a substring of the field. The matching is
 case-insensitive.

 The defined search keys are as follows. Refer to the Formal
 Syntax section for the precise syntactic definitions of the
 arguments.

 <sequence set>
 Messages with message sequence numbers corresponding to the
 specified message sequence number set.

 ALL
 All messages in the mailbox; the default initial key for
 ANDing.

 ANSWERED
 Messages with the \Answered flag set.








Crispin Standards Track [Page 50]

RFC 3501 IMAPv4 March 2003


 BCC <string>
 Messages that contain the specified string in the envelope
 structure's BCC field.

 BEFORE <date>
 Messages whose internal date (disregarding time and timezone)
 is earlier than the specified date.

 BODY <string>
 Messages that contain the specified string in the body of the
 message.

 CC <string>
 Messages that contain the specified string in the envelope
 structure's CC field.

 DELETED
 Messages with the \Deleted flag set.

 DRAFT
 Messages with the \Draft flag set.

 FLAGGED
 Messages with the \Flagged flag set.

 FROM <string>
 Messages that contain the specified string in the envelope
 structure's FROM field.

 HEADER <field-name> <string>
 Messages that have a header with the specified field-name (as
 defined in [RFC-2822]) and that contains the specified string
 in the text of the header (what comes after the colon). If the
 string to search is zero-length, this matches all messages that
 have a header line with the specified field-name regardless of
 the contents.

 KEYWORD <flag>
 Messages with the specified keyword flag set.

 LARGER <n>
 Messages with an [RFC-2822] size larger than the specified
 number of octets.

 NEW
 Messages that have the \Recent flag set but not the \Seen flag.
 This is functionally equivalent to "(RECENT UNSEEN)".




Crispin Standards Track [Page 51]

RFC 3501 IMAPv4 March 2003


 NOT <search-key>
 Messages that do not match the specified search key.

 OLD
 Messages that do not have the \Recent flag set. This is
 functionally equivalent to "NOT RECENT" (as opposed to "NOT
 NEW").

 ON <date>
 Messages whose internal date (disregarding time and timezone)
 is within the specified date.

 OR <search-key1> <search-key2>
 Messages that match either search key.

 RECENT
 Messages that have the \Recent flag set.

 SEEN
 Messages that have the \Seen flag set.

 SENTBEFORE <date>
 Messages whose [RFC-2822] Date: header (disregarding time and
 timezone) is earlier than the specified date.

 SENTON <date>
 Messages whose [RFC-2822] Date: header (disregarding time and
 timezone) is within the specified date.

 SENTSINCE <date>
 Messages whose [RFC-2822] Date: header (disregarding time and
 timezone) is within or later than the specified date.

 SINCE <date>
 Messages whose internal date (disregarding time and timezone)
 is within or later than the specified date.

 SMALLER <n>
 Messages with an [RFC-2822] size smaller than the specified
 number of octets.











Crispin Standards Track [Page 52]

RFC 3501 IMAPv4 March 2003


 SUBJECT <string>
 Messages that contain the specified string in the envelope
 structure's SUBJECT field.

 TEXT <string>
 Messages that contain the specified string in the header or
 body of the message.

 TO <string>
 Messages that contain the specified string in the envelope
 structure's TO field.

 UID <sequence set>
 Messages with unique identifiers corresponding to the specified
 unique identifier set. Sequence set ranges are permitted.

 UNANSWERED
 Messages that do not have the \Answered flag set.

 UNDELETED
 Messages that do not have the \Deleted flag set.

 UNDRAFT
 Messages that do not have the \Draft flag set.

 UNFLAGGED
 Messages that do not have the \Flagged flag set.

 UNKEYWORD <flag>
 Messages that do not have the specified keyword flag set.

 UNSEEN
 Messages that do not have the \Seen flag set.


















Crispin Standards Track [Page 53]

RFC 3501 IMAPv4 March 2003


 Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
 S: * SEARCH 2 84 882
 S: A282 OK SEARCH completed
 C: A283 SEARCH TEXT "string not in mailbox"
 S: * SEARCH
 S: A283 OK SEARCH completed
 C: A284 SEARCH CHARSET UTF-8 TEXT {6}
 C: XXXXXX
 S: * SEARCH 43
 S: A284 OK SEARCH completed

 Note: Since this document is restricted to 7-bit ASCII
 text, it is not possible to show actual UTF-8 data. The
 "XXXXXX" is a placeholder for what would be 6 octets of
 8-bit data in an actual transaction.


6.4.5. FETCH Command

 Arguments: sequence set
 message data item names or macro

 Responses: untagged responses: FETCH

 Result: OK - fetch completed
 NO - fetch error: can't fetch that data
 BAD - command unknown or arguments invalid

 The FETCH command retrieves data associated with a message in the
 mailbox. The data items to be fetched can be either a single atom
 or a parenthesized list.

 Most data items, identified in the formal syntax under the
 msg-att-static rule, are static and MUST NOT change for any
 particular message. Other data items, identified in the formal
 syntax under the msg-att-dynamic rule, MAY change, either as a
 result of a STORE command or due to external events.

 For example, if a client receives an ENVELOPE for a
 message when it already knows the envelope, it can
 safely ignore the newly transmitted envelope.

 There are three macros which specify commonly-used sets of data
 items, and can be used instead of data items. A macro must be
 used by itself, and not in conjunction with other macros or data
 items.





Crispin Standards Track [Page 54]

RFC 3501 IMAPv4 March 2003


 ALL
 Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE)

 FAST
 Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE)

 FULL
 Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE
 BODY)

 The currently defined data items that can be fetched are:

 BODY
 Non-extensible form of BODYSTRUCTURE.

 BODY[<section>]<<partial>>
 The text of a particular body section. The section
 specification is a set of zero or more part specifiers
 delimited by periods. A part specifier is either a part number
 or one of the following: HEADER, HEADER.FIELDS,
 HEADER.FIELDS.NOT, MIME, and TEXT. An empty section
 specification refers to the entire message, including the
 header.

 Every message has at least one part number. Non-[MIME-IMB]
 messages, and non-multipart [MIME-IMB] messages with no
 encapsulated message, only have a part 1.

 Multipart messages are assigned consecutive part numbers, as
 they occur in the message. If a particular part is of type
 message or multipart, its parts MUST be indicated by a period
 followed by the part number within that nested multipart part.

 A part of type MESSAGE/RFC822 also has nested part numbers,
 referring to parts of the MESSAGE part's body.

 The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part
 specifiers can be the sole part specifier or can be prefixed by
 one or more numeric part specifiers, provided that the numeric
 part specifier refers to a part of type MESSAGE/RFC822. The
 MIME part specifier MUST be prefixed by one or more numeric
 part specifiers.

 The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part
 specifiers refer to the [RFC-2822] header of the message or of
 an encapsulated [MIME-IMT] MESSAGE/RFC822 message.
 HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of
 field-name (as defined in [RFC-2822]) names, and return a



Crispin Standards Track [Page 55]

RFC 3501 IMAPv4 March 2003


 subset of the header. The subset returned by HEADER.FIELDS
 contains only those header fields with a field-name that
 matches one of the names in the list; similarly, the subset
 returned by HEADER.FIELDS.NOT contains only the header fields
 with a non-matching field-name. The field-matching is
 case-insensitive but otherwise exact. Subsetting does not
 exclude the [RFC-2822] delimiting blank line between the header
 and the body; the blank line is included in all header fetches,
 except in the case of a message which has no body and no blank
 line.

 The MIME part specifier refers to the [MIME-IMB] header for
 this part.

 The TEXT part specifier refers to the text body of the message,
 omitting the [RFC-2822] header.

 Here is an example of a complex message with some of its
 part specifiers:

 HEADER ([RFC-2822] header of the message)
 TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
 1 TEXT/PLAIN
 2 APPLICATION/OCTET-STREAM
 3 MESSAGE/RFC822
 3.HEADER ([RFC-2822] header of the message)
 3.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
 3.1 TEXT/PLAIN
 3.2 APPLICATION/OCTET-STREAM
 4 MULTIPART/MIXED
 4.1 IMAGE/GIF
 4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
 4.2 MESSAGE/RFC822
 4.2.HEADER ([RFC-2822] header of the message)
 4.2.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
 4.2.1 TEXT/PLAIN
 4.2.2 MULTIPART/ALTERNATIVE
 4.2.2.1 TEXT/PLAIN
 4.2.2.2 TEXT/RICHTEXT


 It is possible to fetch a substring of the designated text.
 This is done by appending an open angle bracket ("<"), the
 octet position of the first desired octet, a period, the
 maximum number of octets desired, and a close angle bracket
 (">") to the part specifier. If the starting octet is beyond
 the end of the text, an empty string is returned.




Crispin Standards Track [Page 56]

RFC 3501 IMAPv4 March 2003


 Any partial fetch that attempts to read beyond the end of the
 text is truncated as appropriate. A partial fetch that starts
 at octet 0 is returned as a partial fetch, even if this
 truncation happened.

 Note: This means that BODY[]<0.2048> of a 1500-octet message
 will return BODY[]<0> with a literal of size 1500, not
 BODY[].

 Note: A substring fetch of a HEADER.FIELDS or
 HEADER.FIELDS.NOT part specifier is calculated after
 subsetting the header.

 The \Seen flag is implicitly set; if this causes the flags to
 change, they SHOULD be included as part of the FETCH responses.

 BODY.PEEK[<section>]<<partial>>
 An alternate form of BODY[<section>] that does not implicitly
 set the \Seen flag.

 BODYSTRUCTURE
 The [MIME-IMB] body structure of the message. This is computed
 by the server by parsing the [MIME-IMB] header fields in the
 [RFC-2822] header and [MIME-IMB] headers.

 ENVELOPE
 The envelope structure of the message. This is computed by the
 server by parsing the [RFC-2822] header into the component
 parts, defaulting various fields as necessary.

 FLAGS
 The flags that are set for this message.

 INTERNALDATE
 The internal date of the message.

 RFC822
 Functionally equivalent to BODY[], differing in the syntax of
 the resulting untagged FETCH data (RFC822 is returned).

 RFC822.HEADER
 Functionally equivalent to BODY.PEEK[HEADER], differing in the
 syntax of the resulting untagged FETCH data (RFC822.HEADER is
 returned).

 RFC822.SIZE
 The [RFC-2822] size of the message.




Crispin Standards Track [Page 57]

RFC 3501 IMAPv4 March 2003


 RFC822.TEXT
 Functionally equivalent to BODY[TEXT], differing in the syntax
 of the resulting untagged FETCH data (RFC822.TEXT is returned).

 UID
 The unique identifier for the message.


 Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
 S: * 2 FETCH ....
 S: * 3 FETCH ....
 S: * 4 FETCH ....
 S: A654 OK FETCH completed


6.4.6. STORE Command

 Arguments: sequence set
 message data item name
 value for message data item

 Responses: untagged responses: FETCH

 Result: OK - store completed
 NO - store error: can't store that data
 BAD - command unknown or arguments invalid

 The STORE command alters data associated with a message in the
 mailbox. Normally, STORE will return the updated value of the
 data with an untagged FETCH response. A suffix of ".SILENT" in
 the data item name prevents the untagged FETCH, and the server
 SHOULD assume that the client has determined the updated value
 itself or does not care about the updated value.

 Note: Regardless of whether or not the ".SILENT" suffix
 was used, the server SHOULD send an untagged FETCH
 response if a change to a message's flags from an
 external source is observed. The intent is that the
 status of the flags is determinate without a race
 condition.











Crispin Standards Track [Page 58]

RFC 3501 IMAPv4 March 2003


 The currently defined data items that can be stored are:

 FLAGS <flag list>
 Replace the flags for the message (other than \Recent) with the
 argument. The new value of the flags is returned as if a FETCH
 of those flags was done.

 FLAGS.SILENT <flag list>
 Equivalent to FLAGS, but without returning a new value.

 +FLAGS <flag list>
 Add the argument to the flags for the message. The new value
 of the flags is returned as if a FETCH of those flags was done.

 +FLAGS.SILENT <flag list>
 Equivalent to +FLAGS, but without returning a new value.

 -FLAGS <flag list>
 Remove the argument from the flags for the message. The new
 value of the flags is returned as if a FETCH of those flags was
 done.

 -FLAGS.SILENT <flag list>
 Equivalent to -FLAGS, but without returning a new value.


 Example: C: A003 STORE 2:4 +FLAGS (\Deleted)
 S: * 2 FETCH (FLAGS (\Deleted \Seen))
 S: * 3 FETCH (FLAGS (\Deleted))
 S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen))
 S: A003 OK STORE completed


6.4.7. COPY Command

 Arguments: sequence set
 mailbox name

 Responses: no specific responses for this command

 Result: OK - copy completed
 NO - copy error: can't copy those messages or to that
 name
 BAD - command unknown or arguments invalid







Crispin Standards Track [Page 59]

RFC 3501 IMAPv4 March 2003


 The COPY command copies the specified message(s) to the end of the
 specified destination mailbox. The flags and internal date of the
 message(s) SHOULD be preserved, and the Recent flag SHOULD be set,
 in the copy.

 If the destination mailbox does not exist, a server SHOULD return
 an error. It SHOULD NOT automatically create the mailbox. Unless
 it is certain that the destination mailbox can not be created, the
 server MUST send the response code "[TRYCREATE]" as the prefix of
 the text of the tagged NO response. This gives a hint to the
 client that it can attempt a CREATE command and retry the COPY if
 the CREATE is successful.

 If the COPY command is unsuccessful for any reason, server
 implementations MUST restore the destination mailbox to its state
 before the COPY attempt.

 Example: C: A003 COPY 2:4 MEETING
 S: A003 OK COPY completed


6.4.8. UID Command

 Arguments: command name
 command arguments

 Responses: untagged responses: FETCH, SEARCH

 Result: OK - UID command completed
 NO - UID command error
 BAD - command unknown or arguments invalid

 The UID command has two forms. In the first form, it takes as its
 arguments a COPY, FETCH, or STORE command with arguments
 appropriate for the associated command. However, the numbers in
 the sequence set argument are unique identifiers instead of
 message sequence numbers. Sequence set ranges are permitted, but
 there is no guarantee that unique identifiers will be contiguous.

 A non-existent unique identifier is ignored without any error
 message generated. Thus, it is possible for a UID FETCH command
 to return an OK without any data or a UID COPY or UID STORE to
 return an OK without performing any operations.

 In the second form, the UID command takes a SEARCH command with
 SEARCH command arguments. The interpretation of the arguments is
 the same as with SEARCH; however, the numbers returned in a SEARCH
 response for a UID SEARCH command are unique identifiers instead



Crispin Standards Track [Page 60]

RFC 3501 IMAPv4 March 2003


 of message sequence numbers. For example, the command UID SEARCH
 1:100 UID 443:557 returns the unique identifiers corresponding to
 the intersection of two sequence sets, the message sequence number
 range 1:100 and the UID range 443:557.

 Note: in the above example, the UID range 443:557
 appears. The same comment about a non-existent unique
 identifier being ignored without any error message also
 applies here. Hence, even if neither UID 443 or 557
 exist, this range is valid and would include an existing
 UID 495.

 Also note that a UID range of 559:* always includes the
 UID of the last message in the mailbox, even if 559 is
 higher than any assigned UID value. This is because the
 contents of a range are independent of the order of the
 range endpoints. Thus, any UID range with * as one of
 the endpoints indicates at least one message (the
 message with the highest numbered UID), unless the
 mailbox is empty.

 The number after the "*" in an untagged FETCH response is always a
 message sequence number, not a unique identifier, even for a UID
 command response. However, server implementations MUST implicitly
 include the UID message data item as part of any FETCH response
 caused by a UID command, regardless of whether a UID was specified
 as a message data item to the FETCH.


 Note: The rule about including the UID message data item as part
 of a FETCH response primarily applies to the UID FETCH and UID
 STORE commands, including a UID FETCH command that does not
 include UID as a message data item. Although it is unlikely that
 the other UID commands will cause an untagged FETCH, this rule
 applies to these commands as well.

 Example: C: A999 UID FETCH 4827313:4828442 FLAGS
 S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
 S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
 S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
 S: A999 OK UID FETCH completed










Crispin Standards Track [Page 61]

RFC 3501 IMAPv4 March 2003


6.5. Client Commands - Experimental/Expansion


6.5.1. X<atom> Command

 Arguments: implementation defined

 Responses: implementation defined

 Result: OK - command completed
 NO - failure
 BAD - command unknown or arguments invalid

 Any command prefixed with an X is an experimental command.
 Commands which are not part of this specification, a standard or
 standards-track revision of this specification, or an
 IESG-approved experimental protocol, MUST use the X prefix.

 Any added untagged responses issued by an experimental command
 MUST also be prefixed with an X. Server implementations MUST NOT
 send any such untagged responses, unless the client requested it
 by issuing the associated experimental command.

 Example: C: a441 CAPABILITY
 S: * CAPABILITY IMAP4rev1 XPIG-LATIN
 S: a441 OK CAPABILITY completed
 C: A442 XPIG-LATIN
 S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
 S: A442 OK XPIG-LATIN ompleted-cay

7. Server Responses

 Server responses are in three forms: status responses, server data,
 and command continuation request. The information contained in a
 server response, identified by "Contents:" in the response
 descriptions below, is described by function, not by syntax. The
 precise syntax of server responses is described in the Formal Syntax
 section.

 The client MUST be prepared to accept any response at all times.

 Status responses can be tagged or untagged. Tagged status responses
 indicate the completion result (OK, NO, or BAD status) of a client
 command, and have a tag matching the command.

 Some status responses, and all server data, are untagged. An
 untagged response is indicated by the token "*" instead of a tag.
 Untagged status responses indicate server greeting, or server status



Crispin Standards Track [Page 62]

RFC 3501 IMAPv4 March 2003


 that does not indicate the completion of a command (for example, an
 impending system shutdown alert). For historical reasons, untagged
 server data responses are also called "unsolicited data", although
 strictly speaking, only unilateral server data is truly
 "unsolicited".

 Certain server data MUST be recorded by the client when it is
 received; this is noted in the description of that data. Such data
 conveys critical information which affects the interpretation of all
 subsequent commands and responses (e.g., updates reflecting the
 creation or destruction of messages).

 Other server data SHOULD be recorded for later reference; if the
 client does not need to record the data, or if recording the data has
 no obvious purpose (e.g., a SEARCH response when no SEARCH command is
 in progress), the data SHOULD be ignored.

 An example of unilateral untagged server data occurs when the IMAP
 connection is in the selected state. In the selected state, the
 server checks the mailbox for new messages as part of command
 execution. Normally, this is part of the execution of every command;
 hence, a NOOP command suffices to check for new messages. If new
 messages are found, the server sends untagged EXISTS and RECENT
 responses reflecting the new size of the mailbox. Server
 implementations that offer multiple simultaneous access to the same
 mailbox SHOULD also send appropriate unilateral untagged FETCH and
 EXPUNGE responses if another agent changes the state of any message
 flags or expunges any messages.

 Command continuation request responses use the token "+" instead of a
 tag. These responses are sent by the server to indicate acceptance
 of an incomplete client command and readiness for the remainder of
 the command.

7.1. Server Responses - Status Responses

 Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD
 can be tagged or untagged. PREAUTH and BYE are always untagged.

 Status responses MAY include an OPTIONAL "response code". A response
 code consists of data inside square brackets in the form of an atom,
 possibly followed by a space and arguments. The response code
 contains additional information or status codes for client software
 beyond the OK/NO/BAD condition, and are defined when there is a
 specific action that a client can take based upon the additional
 information.





Crispin Standards Track [Page 63]

RFC 3501 IMAPv4 March 2003


 The currently defined response codes are:

 ALERT

 The human-readable text contains a special alert that MUST be
 presented to the user in a fashion that calls the user's
 attention to the message.

 BADCHARSET

 Optionally followed by a parenthesized list of charsets. A
 SEARCH failed because the given charset is not supported by
 this implementation. If the optional list of charsets is
 given, this lists the charsets that are supported by this
 implementation.

 CAPABILITY

 Followed by a list of capabilities. This can appear in the
 initial OK or PREAUTH response to transmit an initial
 capabilities list. This makes it unnecessary for a client to
 send a separate CAPABILITY command if it recognizes this
 response.

 PARSE

 The human-readable text represents an error in parsing the
 [RFC-2822] header or [MIME-IMB] headers of a message in the
 mailbox.

 PERMANENTFLAGS

 Followed by a parenthesized list of flags, indicates which of
 the known flags the client can change permanently. Any flags
 that are in the FLAGS untagged response, but not the
 PERMANENTFLAGS list, can not be set permanently. If the client
 attempts to STORE a flag that is not in the PERMANENTFLAGS
 list, the server will either ignore the change or store the
 state change for the remainder of the current session only.
 The PERMANENTFLAGS list can also include the special flag \*,
 which indicates that it is possible to create new keywords by
 attempting to store those flags in the mailbox.









Crispin Standards Track [Page 64]

RFC 3501 IMAPv4 March 2003


 READ-ONLY

 The mailbox is selected read-only, or its access while selected
 has changed from read-write to read-only.

 READ-WRITE

 The mailbox is selected read-write, or its access while
 selected has changed from read-only to read-write.

 TRYCREATE

 An APPEND or COPY attempt is failing because the target mailbox
 does not exist (as opposed to some other reason). This is a
 hint to the client that the operation can succeed if the
 mailbox is first created by the CREATE command.

 UIDNEXT

 Followed by a decimal number, indicates the next unique
 identifier value. Refer to section 2.3.1.1 for more
 information.

 UIDVALIDITY

 Followed by a decimal number, indicates the unique identifier
 validity value. Refer to section 2.3.1.1 for more information.

 UNSEEN

 Followed by a decimal number, indicates the number of the first
 message without the \Seen flag set.

 Additional response codes defined by particular client or server
 implementations SHOULD be prefixed with an "X" until they are
 added to a revision of this protocol. Client implementations
 SHOULD ignore response codes that they do not recognize.

7.1.1. OK Response

 Contents: OPTIONAL response code
 human-readable text

 The OK response indicates an information message from the server.
 When tagged, it indicates successful completion of the associated
 command. The human-readable text MAY be presented to the user as
 an information message. The untagged form indicates an




Crispin Standards Track [Page 65]

RFC 3501 IMAPv4 March 2003


 information-only message; the nature of the information MAY be
 indicated by a response code.

 The untagged form is also used as one of three possible greetings
 at connection startup. It indicates that the connection is not
 yet authenticated and that a LOGIN command is needed.

 Example: S: * OK IMAP4rev1 server ready
 C: A001 LOGIN fred blurdybloop
 S: * OK [ALERT] System shutdown in 10 minutes
 S: A001 OK LOGIN Completed


7.1.2. NO Response

 Contents: OPTIONAL response code
 human-readable text

 The NO response indicates an operational error message from the
 server. When tagged, it indicates unsuccessful completion of the
 associated command. The untagged form indicates a warning; the
 command can still complete successfully. The human-readable text
 describes the condition.

 Example: C: A222 COPY 1:2 owatagusiam
 S: * NO Disk is 98% full, please delete unnecessary data
 S: A222 OK COPY completed
 C: A223 COPY 3:200 blurdybloop
 S: * NO Disk is 98% full, please delete unnecessary data
 S: * NO Disk is 99% full, please delete unnecessary data
 S: A223 NO COPY failed: disk is full


7.1.3. BAD Response

 Contents: OPTIONAL response code
 human-readable text

 The BAD response indicates an error message from the server. When
 tagged, it reports a protocol-level error in the client's command;
 the tag indicates the command that caused the error. The untagged
 form indicates a protocol-level error for which the associated
 command can not be determined; it can also indicate an internal
 server failure. The human-readable text describes the condition.







Crispin Standards Track [Page 66]

RFC 3501 IMAPv4 March 2003


 Example: C: ...very long command line...
 S: * BAD Command line too long
 C: ...empty line...
 S: * BAD Empty command line
 C: A443 EXPUNGE
 S: * BAD Disk crash, attempting salvage to a new disk!
 S: * OK Salvage successful, no data lost
 S: A443 OK Expunge completed


7.1.4. PREAUTH Response

 Contents: OPTIONAL response code
 human-readable text

 The PREAUTH response is always untagged, and is one of three
 possible greetings at connection startup. It indicates that the
 connection has already been authenticated by external means; thus
 no LOGIN command is needed.

 Example: S: * PREAUTH IMAP4rev1 server logged in as Smith


7.1.5. BYE Response

 Contents: OPTIONAL response code
 human-readable text

 The BYE response is always untagged, and indicates that the server
 is about to close the connection. The human-readable text MAY be
 displayed to the user in a status report by the client. The BYE
 response is sent under one of four conditions:

 1) as part of a normal logout sequence. The server will close
 the connection after sending the tagged OK response to the
 LOGOUT command.

 2) as a panic shutdown announcement. The server closes the
 connection immediately.

 3) as an announcement of an inactivity autologout. The server
 closes the connection immediately.

 4) as one of three possible greetings at connection startup,
 indicating that the server is not willing to accept a
 connection from this client. The server closes the
 connection immediately.




Crispin Standards Track [Page 67]

RFC 3501 IMAPv4 March 2003


 The difference between a BYE that occurs as part of a normal
 LOGOUT sequence (the first case) and a BYE that occurs because of
 a failure (the other three cases) is that the connection closes
 immediately in the failure case. In all cases the client SHOULD
 continue to read response data from the server until the
 connection is closed; this will ensure that any pending untagged
 or completion responses are read and processed.

 Example: S: * BYE Autologout; idle for too long

7.2. Server Responses - Server and Mailbox Status

 These responses are always untagged. This is how server and mailbox
 status data are transmitted from the server to the client. Many of
 these responses typically result from a command with the same name.

7.2.1. CAPABILITY Response

 Contents: capability listing

 The CAPABILITY response occurs as a result of a CAPABILITY
 command. The capability listing contains a space-separated
 listing of capability names that the server supports. The
 capability listing MUST include the atom "IMAP4rev1".

 In addition, client and server implementations MUST implement the
 STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS])
 capabilities. See the Security Considerations section for
 important information.

 A capability name which begins with "AUTH=" indicates that the
 server supports that particular authentication mechanism.

 The LOGINDISABLED capability indicates that the LOGIN command is
 disabled, and that the server will respond with a tagged NO
 response to any attempt to use the LOGIN command even if the user
 name and password are valid. An IMAP client MUST NOT issue the
 LOGIN command if the server advertises the LOGINDISABLED
 capability.

 Other capability names indicate that the server supports an
 extension, revision, or amendment to the IMAP4rev1 protocol.
 Server responses MUST conform to this document until the client
 issues a command that uses the associated capability.

 Capability names MUST either begin with "X" or be standard or
 standards-track IMAP4rev1 extensions, revisions, or amendments
 registered with IANA. A server MUST NOT offer unregistered or



Crispin Standards Track [Page 68]

RFC 3501 IMAPv4 March 2003


 non-standard capability names, unless such names are prefixed with
 an "X".

 Client implementations SHOULD NOT require any capability name
 other than "IMAP4rev1", and MUST ignore any unknown capability
 names.

 A server MAY send capabilities automatically, by using the
 CAPABILITY response code in the initial PREAUTH or OK responses,
 and by sending an updated CAPABILITY response code in the tagged
 OK response as part of a successful authentication. It is
 unnecessary for a client to send a separate CAPABILITY command if
 it recognizes these automatic capabilities.

 Example: S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI XPIG-LATIN


7.2.2. LIST Response

 Contents: name attributes
 hierarchy delimiter
 name

 The LIST response occurs as a result of a LIST command. It
 returns a single name that matches the LIST specification. There
 can be multiple LIST responses for a single LIST command.

 Four name attributes are defined:

 \Noinferiors
 It is not possible for any child levels of hierarchy to exist
 under this name; no child levels exist now and none can be
 created in the future.

 \Noselect
 It is not possible to use this name as a selectable mailbox.

 \Marked
 The mailbox has been marked "interesting" by the server; the
 mailbox probably contains messages that have been added since
 the last time the mailbox was selected.

 \Unmarked
 The mailbox does not contain any additional messages since the
 last time the mailbox was selected.






Crispin Standards Track [Page 69]

RFC 3501 IMAPv4 March 2003


 If it is not feasible for the server to determine whether or not
 the mailbox is "interesting", or if the name is a \Noselect name,
 the server SHOULD NOT send either \Marked or \Unmarked.

 The hierarchy delimiter is a character used to delimit levels of
 hierarchy in a mailbox name. A client can use it to create child
 mailboxes, and to search higher or lower levels of naming
 hierarchy. All children of a top-level hierarchy node MUST use
 the same separator character. A NIL hierarchy delimiter means
 that no hierarchy exists; the name is a "flat" name.

 The name represents an unambiguous left-to-right hierarchy, and
 MUST be valid for use as a reference in LIST and LSUB commands.
 Unless \Noselect is indicated, the name MUST also be valid as an
 argument for commands, such as SELECT, that accept mailbox names.

 Example: S: * LIST (\Noselect) "/" ~/Mail/foo


7.2.3. LSUB Response

 Contents: name attributes
 hierarchy delimiter
 name

 The LSUB response occurs as a result of an LSUB command. It
 returns a single name that matches the LSUB specification. There
 can be multiple LSUB responses for a single LSUB command. The
 data is identical in format to the LIST response.

 Example: S: * LSUB () "." #news.comp.mail.misc


7.2.4 STATUS Response

 Contents: name
 status parenthesized list

 The STATUS response occurs as a result of an STATUS command. It
 returns the mailbox name that matches the STATUS specification and
 the requested mailbox status information.

 Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)








Crispin Standards Track [Page 70]

RFC 3501 IMAPv4 March 2003


7.2.5. SEARCH Response

 Contents: zero or more numbers

 The SEARCH response occurs as a result of a SEARCH or UID SEARCH
 command. The number(s) refer to those messages that match the
 search criteria. For SEARCH, these are message sequence numbers;
 for UID SEARCH, these are unique identifiers. Each number is
 delimited by a space.

 Example: S: * SEARCH 2 3 6


7.2.6. FLAGS Response

 Contents: flag parenthesized list

 The FLAGS response occurs as a result of a SELECT or EXAMINE
 command. The flag parenthesized list identifies the flags (at a
 minimum, the system-defined flags) that are applicable for this
 mailbox. Flags other than the system flags can also exist,
 depending on server implementation.

 The update from the FLAGS response MUST be recorded by the client.

 Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)


7.3. Server Responses - Mailbox Size

 These responses are always untagged. This is how changes in the size
 of the mailbox are transmitted from the server to the client.
 Immediately following the "*" token is a number that represents a
 message count.

7.3.1. EXISTS Response

 Contents: none

 The EXISTS response reports the number of messages in the mailbox.
 This response occurs as a result of a SELECT or EXAMINE command,
 and if the size of the mailbox changes (e.g., new messages).

 The update from the EXISTS response MUST be recorded by the
 client.

 Example: S: * 23 EXISTS




Crispin Standards Track [Page 71]

RFC 3501 IMAPv4 March 2003


7.3.2. RECENT Response

 Contents: none

 The RECENT response reports the number of messages with the
 \Recent flag set. This response occurs as a result of a SELECT or
 EXAMINE command, and if the size of the mailbox changes (e.g., new
 messages).

 Note: It is not guaranteed that the message sequence
 numbers of recent messages will be a contiguous range of
 the highest n messages in the mailbox (where n is the
 value reported by the RECENT response). Examples of
 situations in which this is not the case are: multiple
 clients having the same mailbox open (the first session
 to be notified will see it as recent, others will
 probably see it as non-recent), and when the mailbox is
 re-ordered by a non-IMAP agent.

 The only reliable way to identify recent messages is to
 look at message flags to see which have the \Recent flag
 set, or to do a SEARCH RECENT.

 The update from the RECENT response MUST be recorded by the
 client.

 Example: S: * 5 RECENT


7.4. Server Responses - Message Status

 These responses are always untagged. This is how message data are
 transmitted from the server to the client, often as a result of a
 command with the same name. Immediately following the "*" token is a
 number that represents a message sequence number.

7.4.1. EXPUNGE Response

 Contents: none

 The EXPUNGE response reports that the specified message sequence
 number has been permanently removed from the mailbox. The message
 sequence number for each successive message in the mailbox is
 immediately decremented by 1, and this decrement is reflected in
 message sequence numbers in subsequent responses (including other
 untagged EXPUNGE responses).





Crispin Standards Track [Page 72]

RFC 3501 IMAPv4 March 2003


 The EXPUNGE response also decrements the number of messages in the
 mailbox; it is not necessary to send an EXISTS response with the
 new value.

 As a result of the immediate decrement rule, message sequence
 numbers that appear in a set of successive EXPUNGE responses
 depend upon whether the messages are removed starting from lower
 numbers to higher numbers, or from higher numbers to lower
 numbers. For example, if the last 5 messages in a 9-message
 mailbox are expunged, a "lower to higher" server will send five
 untagged EXPUNGE responses for message sequence number 5, whereas
 a "higher to lower server" will send successive untagged EXPUNGE
 responses for message sequence numbers 9, 8, 7, 6, and 5.

 An EXPUNGE response MUST NOT be sent when no command is in
 progress, nor while responding to a FETCH, STORE, or SEARCH
 command. This rule is necessary to prevent a loss of
 synchronization of message sequence numbers between client and
 server. A command is not "in progress" until the complete command
 has been received; in particular, a command is not "in progress"
 during the negotiation of command continuation.

 Note: UID FETCH, UID STORE, and UID SEARCH are different
 commands from FETCH, STORE, and SEARCH. An EXPUNGE
 response MAY be sent during a UID command.

 The update from the EXPUNGE response MUST be recorded by the
 client.

 Example: S: * 44 EXPUNGE


7.4.2. FETCH Response

 Contents: message data

 The FETCH response returns data about a message to the client.
 The data are pairs of data item names and their values in
 parentheses. This response occurs as the result of a FETCH or
 STORE command, as well as by unilateral server decision (e.g.,
 flag updates).

 The current data items are:

 BODY
 A form of BODYSTRUCTURE without extension data.





Crispin Standards Track [Page 73]

RFC 3501 IMAPv4 March 2003


 BODY[<section>]<<origin octet>>
 A string expressing the body contents of the specified section.
 The string SHOULD be interpreted by the client according to the
 content transfer encoding, body type, and subtype.

 If the origin octet is specified, this string is a substring of
 the entire body contents, starting at that origin octet. This
 means that BODY[]<0> MAY be truncated, but BODY[] is NEVER
 truncated.

 Note: The origin octet facility MUST NOT be used by a server
 in a FETCH response unless the client specifically requested
 it by means of a FETCH of a BODY[<section>]<<partial>> data
 item.

 8-bit textual data is permitted if a [CHARSET] identifier is
 part of the body parameter parenthesized list for this section.
 Note that headers (part specifiers HEADER or MIME, or the
 header portion of a MESSAGE/RFC822 part), MUST be 7-bit; 8-bit
 characters are not permitted in headers. Note also that the
 [RFC-2822] delimiting blank line between the header and the
 body is not affected by header line subsetting; the blank line
 is always included as part of header data, except in the case
 of a message which has no body and no blank line.

 Non-textual data such as binary data MUST be transfer encoded
 into a textual form, such as BASE64, prior to being sent to the
 client. To derive the original binary data, the client MUST
 decode the transfer encoded string.

 BODYSTRUCTURE
 A parenthesized list that describes the [MIME-IMB] body
 structure of a message. This is computed by the server by
 parsing the [MIME-IMB] header fields, defaulting various fields
 as necessary.

 For example, a simple text message of 48 lines and 2279 octets
 can have a body structure of: ("TEXT" "PLAIN" ("CHARSET"
 "US-ASCII") NIL NIL "7BIT" 2279 48)

 Multiple parts are indicated by parenthesis nesting. Instead
 of a body type as the first element of the parenthesized list,
 there is a sequence of one or more nested body structures. The
 second element of the parenthesized list is the multipart
 subtype (mixed, digest, parallel, alternative, etc.).






Crispin Standards Track [Page 74]

RFC 3501 IMAPv4 March 2003


 For example, a two part message consisting of a text and a
 BASE64-encoded text attachment can have a body structure of:
 (("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152
 23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff")
 "<960723163407.20117h@cac.washington.edu>" "Compiler diff"
 "BASE64" 4554 73) "MIXED")

 Extension data follows the multipart subtype. Extension data
 is never returned with the BODY fetch, but can be returned with
 a BODYSTRUCTURE fetch. Extension data, if present, MUST be in
 the defined order. The extension data of a multipart body part
 are in the following order:

 body parameter parenthesized list
 A parenthesized list of attribute/value pairs [e.g., ("foo"
 "bar" "baz" "rag") where "bar" is the value of "foo", and
 "rag" is the value of "baz"] as defined in [MIME-IMB].

 body disposition
 A parenthesized list, consisting of a disposition type
 string, followed by a parenthesized list of disposition
 attribute/value pairs as defined in [DISPOSITION].

 body language
 A string or parenthesized list giving the body language
 value as defined in [LANGUAGE-TAGS].

 body location
 A string list giving the body content URI as defined in
 [LOCATION].

 Any following extension data are not yet defined in this
 version of the protocol. Such extension data can consist of
 zero or more NILs, strings, numbers, or potentially nested
 parenthesized lists of such data. Client implementations that
 do a BODYSTRUCTURE fetch MUST be prepared to accept such
 extension data. Server implementations MUST NOT send such
 extension data until it has been defined by a revision of this
 protocol.

 The basic fields of a non-multipart body part are in the
 following order:

 body type
 A string giving the content media type name as defined in
 [MIME-IMB].





Crispin Standards Track [Page 75]

RFC 3501 IMAPv4 March 2003


 body subtype
 A string giving the content subtype name as defined in
 [MIME-IMB].

 body parameter parenthesized list
 A parenthesized list of attribute/value pairs [e.g., ("foo"
 "bar" "baz" "rag") where "bar" is the value of "foo" and
 "rag" is the value of "baz"] as defined in [MIME-IMB].

 body id
 A string giving the content id as defined in [MIME-IMB].

 body description
 A string giving the content description as defined in
 [MIME-IMB].

 body encoding
 A string giving the content transfer encoding as defined in
 [MIME-IMB].

 body size
 A number giving the size of the body in octets. Note that
 this size is the size in its transfer encoding and not the
 resulting size after any decoding.

 A body type of type MESSAGE and subtype RFC822 contains,
 immediately after the basic fields, the envelope structure,
 body structure, and size in text lines of the encapsulated
 message.

 A body type of type TEXT contains, immediately after the basic
 fields, the size of the body in text lines. Note that this
 size is the size in its content transfer encoding and not the
 resulting size after any decoding.

 Extension data follows the basic fields and the type-specific
 fields listed above. Extension data is never returned with the
 BODY fetch, but can be returned with a BODYSTRUCTURE fetch.
 Extension data, if present, MUST be in the defined order.

 The extension data of a non-multipart body part are in the
 following order:

 body MD5
 A string giving the body MD5 value as defined in [MD5].






Crispin Standards Track [Page 76]

RFC 3501 IMAPv4 March 2003


 body disposition
 A parenthesized list with the same content and function as
 the body disposition for a multipart body part.

 body language
 A string or parenthesized list giving the body language
 value as defined in [LANGUAGE-TAGS].

 body location
 A string list giving the body content URI as defined in
 [LOCATION].

 Any following extension data are not yet defined in this
 version of the protocol, and would be as described above under
 multipart extension data.

 ENVELOPE
 A parenthesized list that describes the envelope structure of a
 message. This is computed by the server by parsing the
 [RFC-2822] header into the component parts, defaulting various
 fields as necessary.

 The fields of the envelope structure are in the following
 order: date, subject, from, sender, reply-to, to, cc, bcc,
 in-reply-to, and message-id. The date, subject, in-reply-to,
 and message-id fields are strings. The from, sender, reply-to,
 to, cc, and bcc fields are parenthesized lists of address
 structures.

 An address structure is a parenthesized list that describes an
 electronic mail address. The fields of an address structure
 are in the following order: personal name, [SMTP]
 at-domain-list (source route), mailbox name, and host name.

 [] group syntax is indicated by a special form of
 address structure in which the host name field is NIL. If the
 mailbox name field is also NIL, this is an end of group marker
 (semi-colon in RFC 822 syntax). If the mailbox name field is
 non-NIL, this is a start of group marker, and the mailbox name
 field holds the group name phrase.

 If the Date, Subject, In-Reply-To, and Message-ID header lines
 are absent in the [RFC-2822] header, the corresponding member
 of the envelope is NIL; if these header lines are present but
 empty the corresponding member of the envelope is the empty
 string.





Crispin Standards Track [Page 77]

RFC 3501 IMAPv4 March 2003


 Note: some servers may return a NIL envelope member in the
 "present but empty" case. Clients SHOULD treat NIL and
 empty string as identical.

 Note: [RFC-2822] requires that all messages have a valid
 Date header. Therefore, the date member in the envelope can
 not be NIL or the empty string.

 Note: [RFC-2822] requires that the In-Reply-To and
 Message-ID headers, if present, have non-empty content.
 Therefore, the in-reply-to and message-id members in the
 envelope can not be the empty string.

 If the From, To, cc, and bcc header lines are absent in the
 [RFC-2822] header, or are present but empty, the corresponding
 member of the envelope is NIL.

 If the Sender or Reply-To lines are absent in the [RFC-2822]
 header, or are present but empty, the server sets the
 corresponding member of the envelope to be the same value as
 the from member (the client is not expected to know to do
 this).

 Note: [RFC-2822] requires that all messages have a valid
 From header. Therefore, the from, sender, and reply-to
 members in the envelope can not be NIL.

 FLAGS
 A parenthesized list of flags that are set for this message.

 INTERNALDATE
 A string representing the internal date of the message.

 RFC822
 Equivalent to BODY[].

 RFC822.HEADER
 Equivalent to BODY[HEADER]. Note that this did not result in
 \Seen being set, because RFC822.HEADER response data occurs as
 a result of a FETCH of RFC822.HEADER. BODY[HEADER] response
 data occurs as a result of a FETCH of BODY[HEADER] (which sets
 \Seen) or BODY.PEEK[HEADER] (which does not set \Seen).

 RFC822.SIZE
 A number expressing the [RFC-2822] size of the message.






Crispin Standards Track [Page 78]

RFC 3501 IMAPv4 March 2003


 RFC822.TEXT
 Equivalent to BODY[TEXT].

 UID
 A number expressing the unique identifier of the message.


 Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)


7.5. Server Responses - Command Continuation Request

 The command continuation request response is indicated by a "+" token
 instead of a tag. This form of response indicates that the server is
 ready to accept the continuation of a command from the client. The
 remainder of this response is a line of text.

 This response is used in the AUTHENTICATE command to transmit server
 data to the client, and request additional client data. This
 response is also used if an argument to any command is a literal.

 The client is not permitted to send the octets of the literal unless
 the server indicates that it is expected. This permits the server to
 process commands and reject errors on a line-by-line basis. The
 remainder of the command, including the CRLF that terminates a
 command, follows the octets of the literal. If there are any
 additional command arguments, the literal octets are followed by a
 space and those arguments.

 Example: C: A001 LOGIN {11}
 S: + Ready for additional command text
 C: FRED FOOBAR {7}
 S: + Ready for additional command text
 C: fat man
 S: A001 OK LOGIN completed
 C: A044 BLURDYBLOOP {102856}
 S: A044 BAD No such command as "BLURDYBLOOP"














Crispin Standards Track [Page 79]

RFC 3501 IMAPv4 March 2003


8. Sample IMAP4rev1 connection

 The following is a transcript of an IMAP4rev1 connection. A long
 line in this sample is broken for editorial clarity.

S: * OK IMAP4rev1 Service Ready
C: a001 login mrc secret
S: a001 OK LOGIN completed
C: a002 select inbox
S: * 18 EXISTS
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * 2 RECENT
S: * OK [UNSEEN 17] Message 17 is the first unseen message
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: a002 OK [READ-WRITE] SELECT completed
C: a003 fetch 12 full
S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700"
 RFC822.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)"
 "IMAP4rev1 WG mtg summary and minutes"
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 ((NIL NIL "imap" "cac.washington.edu"))
 ((NIL NIL "minutes" "CNRI.Reston.VA.US")
 ("John Klensin" NIL "KLENSIN" "MIT.EDU")) NIL NIL
 "<B27397-0100000@cac.washington.edu>")
 BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028
 92))
S: a003 OK FETCH completed
C: a004 fetch 12 body[header]
S: * 12 FETCH (BODY[HEADER] {342}
S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT)
S: From: Terry Gray <gray@cac.washington.edu>
S: Subject: IMAP4rev1 WG mtg summary and minutes
S: To: imap@cac.washington.edu
S: cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@MIT.EDU>
S: Message-Id: <B27397-0100000@cac.washington.edu>
S: MIME-Version: 1.0
S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
S:
S: )
S: a004 OK FETCH completed
C: a005 store 12 +flags \deleted
S: * 12 FETCH (FLAGS (\Seen \Deleted))
S: a005 OK +FLAGS completed
C: a006 logout
S: * BYE IMAP4rev1 server terminating connection
S: a006 OK LOGOUT completed



Crispin Standards Track [Page 80]

RFC 3501 IMAPv4 March 2003


9. Formal Syntax

 The following syntax specification uses the Augmented Backus-Naur
 Form (ABNF) notation as specified in [ABNF].

 In the case of alternative or optional rules in which a later rule
 overlaps an earlier rule, the rule which is listed earlier MUST take
 priority. For example, "\Seen" when parsed as a flag is the \Seen
 flag name and not a flag-extension, even though "\Seen" can be parsed
 as a flag-extension. Some, but not all, instances of this rule are
 noted below.

 Note: [ABNF] rules MUST be followed strictly; in
 particular:

 (1) Except as noted otherwise, all alphabetic characters
 are case-insensitive. The use of upper or lower case
 characters to define token strings is for editorial clarity
 only. Implementations MUST accept these strings in a
 case-insensitive fashion.

 (2) In all cases, SP refers to exactly one space. It is
 NOT permitted to substitute TAB, insert additional spaces,
 or otherwise treat SP as being equivalent to LWSP.

 (3) The ASCII NUL character, %x00, MUST NOT be used at any
 time.

address = "(" addr-name SP addr-adl SP addr-mailbox SP
 addr-host ")"

addr-adl = nstring
 ; Holds route from [RFC-2822] route-addr if
 ; non-NIL

addr-host = nstring
 ; NIL indicates [RFC-2822] group syntax.
 ; Otherwise, holds [RFC-2822] domain name

addr-mailbox = nstring
 ; NIL indicates end of [RFC-2822] group; if
 ; non-NIL and addr-host is NIL, holds
 ; [RFC-2822] group name.
 ; Otherwise, holds [RFC-2822] local-part
 ; after removing [RFC-2822] quoting






Crispin Standards Track [Page 81]

RFC 3501 IMAPv4 March 2003


addr-name = nstring
 ; If non-NIL, holds phrase from [RFC-2822]
 ; mailbox after removing [RFC-2822] quoting

append = "APPEND" SP mailbox [SP flag-list] [SP date-time] SP
 literal

astring = 1*ASTRING-CHAR / string

ASTRING-CHAR = ATOM-CHAR / resp-specials

atom = 1*ATOM-CHAR

ATOM-CHAR = <any CHAR except atom-specials>

atom-specials = "(" / ")" / "{" / SP / CTL / list-wildcards /
 quoted-specials / resp-specials

authenticate = "AUTHENTICATE" SP auth-type *(CRLF base64)

auth-type = atom
 ; Defined by [SASL]

base64 = *(4base64-char) [base64-terminal]

base64-char = ALPHA / DIGIT / "+" / "/"
 ; Case-sensitive

base64-terminal = (2base64-char "==") / (3base64-char "=")

body = "(" (body-type-1part / body-type-mpart) ")"

body-extension = nstring / number /
 "(" body-extension *(SP body-extension) ")"
 ; Future expansion. Client implementations
 ; MUST accept body-extension fields. Server
 ; implementations MUST NOT generate
 ; body-extension fields except as defined by
 ; future standard or standards-track
 ; revisions of this specification.

body-ext-1part = body-fld-md5 [SP body-fld-dsp [SP body-fld-lang
 [SP body-fld-loc *(SP body-extension)]]]
 ; MUST NOT be returned on non-extensible
 ; "BODY" fetch






Crispin Standards Track [Page 82]

RFC 3501 IMAPv4 March 2003


body-ext-mpart = body-fld-param [SP body-fld-dsp [SP body-fld-lang
 [SP body-fld-loc *(SP body-extension)]]]
 ; MUST NOT be returned on non-extensible
 ; "BODY" fetch

body-fields = body-fld-param SP body-fld-id SP body-fld-desc SP
 body-fld-enc SP body-fld-octets

body-fld-desc = nstring

body-fld-dsp = "(" string SP body-fld-param ")" / nil

body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
 "QUOTED-PRINTABLE") DQUOTE) / string

body-fld-id = nstring

body-fld-lang = nstring / "(" string *(SP string) ")"

body-fld-loc = nstring

body-fld-lines = number

body-fld-md5 = nstring

body-fld-octets = number

body-fld-param = "(" string SP string *(SP string SP string) ")" / nil

body-type-1part = (body-type-basic / body-type-msg / body-type-text)
 [SP body-ext-1part]

body-type-basic = media-basic SP body-fields
 ; MESSAGE subtype MUST NOT be "RFC822"

body-type-mpart = 1*body SP media-subtype
 [SP body-ext-mpart]

body-type-msg = media-message SP body-fields SP envelope
 SP body SP body-fld-lines

body-type-text = media-text SP body-fields SP body-fld-lines

capability = ("AUTH=" auth-type) / atom
 ; New capabilities MUST begin with "X" or be
 ; registered with IANA as standard or
 ; standards-track




Crispin Standards Track [Page 83]

RFC 3501 IMAPv4 March 2003


capability-data = "CAPABILITY" *(SP capability) SP "IMAP4rev1"
 *(SP capability)
 ; Servers MUST implement the STARTTLS, AUTH=PLAIN,
 ; and LOGINDISABLED capabilities
 ; Servers which offer RFC 1730 compatibility MUST
 ; list "IMAP4" as the first capability.

CHAR8 = %x01-ff
 ; any OCTET except NUL, %x00

command = tag SP (command-any / command-auth / command-nonauth /
 command-select) CRLF
 ; Modal based on state

command-any = "CAPABILITY" / "LOGOUT" / "NOOP" / x-command
 ; Valid in all states

command-auth = append / create / delete / examine / list / lsub /
 rename / select / status / subscribe / unsubscribe
 ; Valid only in Authenticated or Selected state

command-nonauth = login / authenticate / "STARTTLS"
 ; Valid only when in Not Authenticated state

command-select = "CHECK" / "CLOSE" / "EXPUNGE" / copy / fetch / store /
 uid / search
 ; Valid only when in Selected state

continue-req = "+" SP (resp-text / base64) CRLF

copy = "COPY" SP sequence-set SP mailbox

create = "CREATE" SP mailbox
 ; Use of INBOX gives a NO error

date = date-text / DQUOTE date-text DQUOTE

date-day = 1*2DIGIT
 ; Day of month

date-day-fixed = (SP DIGIT) / 2DIGIT
 ; Fixed-format version of date-day

date-month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" /
 "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"

date-text = date-day "-" date-month "-" date-year




Crispin Standards Track [Page 84]

RFC 3501 IMAPv4 March 2003


date-year = 4DIGIT

date-time = DQUOTE date-day-fixed "-" date-month "-" date-year
 SP time SP zone DQUOTE

delete = "DELETE" SP mailbox
 ; Use of INBOX gives a NO error

digit-nz = %x31-39
 ; 1-9

envelope = "(" env-date SP env-subject SP env-from SP
 env-sender SP env-reply-to SP env-to SP env-cc SP
 env-bcc SP env-in-reply-to SP env-message-id ")"

env-bcc = "(" 1*address ")" / nil

env-cc = "(" 1*address ")" / nil

env-date = nstring

env-from = "(" 1*address ")" / nil

env-in-reply-to = nstring

env-message-id = nstring

env-reply-to = "(" 1*address ")" / nil

env-sender = "(" 1*address ")" / nil

env-subject = nstring

env-to = "(" 1*address ")" / nil

examine = "EXAMINE" SP mailbox

fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / "FAST" /
 fetch-att / "(" fetch-att *(SP fetch-att) ")")

fetch-att = "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
 "RFC822" [".HEADER" / ".SIZE" / ".TEXT"] /
 "BODY" ["STRUCTURE"] / "UID" /
 "BODY" section ["<" number "." nz-number ">"] /
 "BODY.PEEK" section ["<" number "." nz-number ">"]






Crispin Standards Track [Page 85]

RFC 3501 IMAPv4 March 2003


flag = "\Answered" / "\Flagged" / "\Deleted" /
 "\Seen" / "\Draft" / flag-keyword / flag-extension
 ; Does not include "\Recent"

flag-extension = "\" atom
 ; Future expansion. Client implementations
 ; MUST accept flag-extension flags. Server
 ; implementations MUST NOT generate
 ; flag-extension flags except as defined by
 ; future standard or standards-track
 ; revisions of this specification.

flag-fetch = flag / "\Recent"

flag-keyword = atom

flag-list = "(" [flag *(SP flag)] ")"

flag-perm = flag / "\*"

greeting = "*" SP (resp-cond-auth / resp-cond-bye) CRLF

header-fld-name = astring

header-list = "(" header-fld-name *(SP header-fld-name) ")"

list = "LIST" SP mailbox SP list-mailbox

list-mailbox = 1*list-char / string

list-char = ATOM-CHAR / list-wildcards / resp-specials

list-wildcards = "%" / "*"

literal = "{" number "}" CRLF *CHAR8
 ; Number represents the number of CHAR8s

login = "LOGIN" SP userid SP password

lsub = "LSUB" SP mailbox SP list-mailbox











Crispin Standards Track [Page 86]

RFC 3501 IMAPv4 March 2003


mailbox = "INBOX" / astring
 ; INBOX is case-insensitive. All case variants of
 ; INBOX (e.g., "iNbOx") MUST be interpreted as INBOX
 ; not as an astring. An astring which consists of
 ; the case-insensitive sequence "I" "N" "B" "O" "X"
 ; is considered to be INBOX and not an astring.
 ; Refer to section 5.1 for further
 ; semantic details of mailbox names.

mailbox-data = "FLAGS" SP flag-list / "LIST" SP mailbox-list /
 "LSUB" SP mailbox-list / "SEARCH" *(SP nz-number) /
 "STATUS" SP mailbox SP "(" [status-att-list] ")" /
 number SP "EXISTS" / number SP "RECENT"

mailbox-list = "(" [mbx-list-flags] ")" SP
 (DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox

mbx-list-flags = *(mbx-list-oflag SP) mbx-list-sflag
 *(SP mbx-list-oflag) /
 mbx-list-oflag *(SP mbx-list-oflag)

mbx-list-oflag = "\Noinferiors" / flag-extension
 ; Other flags; multiple possible per LIST response

mbx-list-sflag = "\Noselect" / "\Marked" / "\Unmarked"
 ; Selectability flags; only one per LIST response

media-basic = ((DQUOTE ("APPLICATION" / "AUDIO" / "IMAGE" /
 "MESSAGE" / "VIDEO") DQUOTE) / string) SP
 media-subtype
 ; Defined in [MIME-IMT]

media-message = DQUOTE "MESSAGE" DQUOTE SP DQUOTE "RFC822" DQUOTE
 ; Defined in [MIME-IMT]

media-subtype = string
 ; Defined in [MIME-IMT]

media-text = DQUOTE "TEXT" DQUOTE SP media-subtype
 ; Defined in [MIME-IMT]

message-data = nz-number SP ("EXPUNGE" / ("FETCH" SP msg-att))

msg-att = "(" (msg-att-dynamic / msg-att-static)
 *(SP (msg-att-dynamic / msg-att-static)) ")"

msg-att-dynamic = "FLAGS" SP "(" [flag-fetch *(SP flag-fetch)] ")"
 ; MAY change for a message



Crispin Standards Track [Page 87]

RFC 3501 IMAPv4 March 2003


msg-att-static = "ENVELOPE" SP envelope / "INTERNALDATE" SP date-time /
 "RFC822" [".HEADER" / ".TEXT"] SP nstring /
 "RFC822.SIZE" SP number /
 "BODY" ["STRUCTURE"] SP body /
 "BODY" section ["<" number ">"] SP nstring /
 "UID" SP uniqueid
 ; MUST NOT change for a message

nil = "NIL"

nstring = string / nil

number = 1*DIGIT
 ; Unsigned 32-bit integer
 ; (0 <= n < 4,294,967,296)

nz-number = digit-nz *DIGIT
 ; Non-zero unsigned 32-bit integer
 ; (0 < n < 4,294,967,296)

password = astring

quoted = DQUOTE *QUOTED-CHAR DQUOTE

QUOTED-CHAR = <any TEXT-CHAR except quoted-specials> /
 "\" quoted-specials

quoted-specials = DQUOTE / "\"

rename = "RENAME" SP mailbox SP mailbox
 ; Use of INBOX as a destination gives a NO error

response = *(continue-req / response-data) response-done

response-data = "*" SP (resp-cond-state / resp-cond-bye /
 mailbox-data / message-data / capability-data) CRLF

response-done = response-tagged / response-fatal

response-fatal = "*" SP resp-cond-bye CRLF
 ; Server closes connection immediately

response-tagged = tag SP resp-cond-state CRLF

resp-cond-auth = ("OK" / "PREAUTH") SP resp-text
 ; Authentication condition





Crispin Standards Track [Page 88]

RFC 3501 IMAPv4 March 2003


resp-cond-bye = "BYE" SP resp-text

resp-cond-state = ("OK" / "NO" / "BAD") SP resp-text
 ; Status condition

resp-specials = "]"

resp-text = ["[" resp-text-code "]" SP] text

resp-text-code = "ALERT" /
 "BADCHARSET" [SP "(" astring *(SP astring) ")" ] /
 capability-data / "PARSE" /
 "PERMANENTFLAGS" SP "("
 [flag-perm *(SP flag-perm)] ")" /
 "READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
 "UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number /
 "UNSEEN" SP nz-number /
 atom [SP 1*<any TEXT-CHAR except "]">]

search = "SEARCH" [SP "CHARSET" SP astring] 1*(SP search-key)
 ; CHARSET argument to MUST be registered with IANA

search-key = "ALL" / "ANSWERED" / "BCC" SP astring /
 "BEFORE" SP date / "BODY" SP astring /
 "CC" SP astring / "DELETED" / "FLAGGED" /
 "FROM" SP astring / "KEYWORD" SP flag-keyword /
 "NEW" / "OLD" / "ON" SP date / "RECENT" / "SEEN" /
 "SINCE" SP date / "SUBJECT" SP astring /
 "TEXT" SP astring / "TO" SP astring /
 "UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
 "UNKEYWORD" SP flag-keyword / "UNSEEN" /
 ; Above this line were in [IMAP2]
 "DRAFT" / "HEADER" SP header-fld-name SP astring /
 "LARGER" SP number / "NOT" SP search-key /
 "OR" SP search-key SP search-key /
 "SENTBEFORE" SP date / "SENTON" SP date /
 "SENTSINCE" SP date / "SMALLER" SP number /
 "UID" SP sequence-set / "UNDRAFT" / sequence-set /
 "(" search-key *(SP search-key) ")"

section = "[" [section-spec] "]"

section-msgtext = "HEADER" / "HEADER.FIELDS" [".NOT"] SP header-list /
 "TEXT"
 ; top-level or MESSAGE/RFC822 part

section-part = nz-number *("." nz-number)
 ; body part nesting



Crispin Standards Track [Page 89]

RFC 3501 IMAPv4 March 2003


section-spec = section-msgtext / (section-part ["." section-text])

section-text = section-msgtext / "MIME"
 ; text other than actual body part (headers, etc.)

select = "SELECT" SP mailbox

seq-number = nz-number / "*"
 ; message sequence number (COPY, FETCH, STORE
 ; commands) or unique identifier (UID COPY,
 ; UID FETCH, UID STORE commands).
 ; * represents the largest number in use. In
 ; the case of message sequence numbers, it is
 ; the number of messages in a non-empty mailbox.
 ; In the case of unique identifiers, it is the
 ; unique identifier of the last message in the
 ; mailbox or, if the mailbox is empty, the
 ; mailbox's current UIDNEXT value.
 ; The server should respond with a tagged BAD
 ; response to a command that uses a message
 ; sequence number greater than the number of
 ; messages in the selected mailbox. This
 ; includes "*" if the selected mailbox is empty.

seq-range = seq-number ":" seq-number
 ; two seq-number values and all values between
 ; these two regardless of order.
 ; Example: 2:4 and 4:2 are equivalent and indicate
 ; values 2, 3, and 4.
 ; Example: a unique identifier sequence range of
 ; 3291:* includes the UID of the last message in
 ; the mailbox, even if that value is less than 3291.

sequence-set = (seq-number / seq-range) *("," sequence-set)
 ; set of seq-number values, regardless of order.
 ; Servers MAY coalesce overlaps and/or execute the
 ; sequence in any order.
 ; Example: a message sequence number set of
 ; 2,4:7,9,12:* for a mailbox with 15 messages is
 ; equivalent to 2,4,5,6,7,9,12,13,14,15
 ; Example: a message sequence number set of *:4,5:7
 ; for a mailbox with 10 messages is equivalent to
 ; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and
 ; overlap coalesced to be 4,5,6,7,8,9,10.

status = "STATUS" SP mailbox SP
 "(" status-att *(SP status-att) ")"




Crispin Standards Track [Page 90]

RFC 3501 IMAPv4 March 2003


status-att = "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" /
 "UNSEEN"

status-att-list = status-att SP number *(SP status-att SP number)

store = "STORE" SP sequence-set SP store-att-flags

store-att-flags = (["+" / "-"] "FLAGS" [".SILENT"]) SP
 (flag-list / (flag *(SP flag)))

string = quoted / literal

subscribe = "SUBSCRIBE" SP mailbox

tag = 1*<any ASTRING-CHAR except "+">

text = 1*TEXT-CHAR

TEXT-CHAR = <any CHAR except CR and LF>

time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
 ; Hours minutes seconds

uid = "UID" SP (copy / fetch / search / store)
 ; Unique identifiers used instead of message
 ; sequence numbers

uniqueid = nz-number
 ; Strictly ascending

unsubscribe = "UNSUBSCRIBE" SP mailbox

userid = astring

x-command = "X" atom <experimental command arguments>

zone = ("+" / "-") 4DIGIT
 ; Signed four-digit value of hhmm representing
 ; hours and minutes east of Greenwich (that is,
 ; the amount that the given time differs from
 ; Universal Time). Subtracting the timezone
 ; from the given time will give the UT form.
 ; The Universal Time zone is "+0000".








Crispin Standards Track [Page 91]

RFC 3501 IMAPv4 March 2003


10. Author's Note

 This document is a revision or rewrite of earlier documents, and
 supercedes the protocol specification in those documents: RFC 2060,
 RFC 1730, unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.

11. Security Considerations

 IMAP4rev1 protocol transactions, including electronic mail data, are
 sent in the clear over the network unless protection from snooping is
 negotiated. This can be accomplished either by the use of STARTTLS,
 negotiated privacy protection in the AUTHENTICATE command, or some
 other protection mechanism.

11.1. STARTTLS Security Considerations

 The specification of the STARTTLS command and LOGINDISABLED
 capability in this document replaces that in [IMAP-TLS]. [IMAP-TLS]
 remains normative for the PLAIN [SASL] authenticator.

 IMAP client and server implementations MUST implement the
 TLS_RSA_WITH_RC4_128_MD5 [TLS] cipher suite, and SHOULD implement the
 TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA [TLS] cipher suite. This is
 important as it assures that any two compliant implementations can be
 configured to interoperate. All other cipher suites are OPTIONAL.
 Note that this is a change from section 2.1 of [IMAP-TLS].

 During the [TLS] negotiation, the client MUST check its understanding
 of the server hostname against the server's identity as presented in
 the server Certificate message, in order to prevent man-in-the-middle
 attacks. If the match fails, the client SHOULD either ask for
 explicit user confirmation, or terminate the connection and indicate
 that the server's identity is suspect. Matching is performed
 according to these rules:

 The client MUST use the server hostname it used to open the
 connection as the value to compare against the server name
 as expressed in the server certificate. The client MUST
 NOT use any form of the server hostname derived from an
 insecure remote source (e.g., insecure DNS lookup). CNAME
 canonicalization is not done.

 If a subjectAltName extension of type dNSName is present in
 the certificate, it SHOULD be used as the source of the
 server's identity.

 Matching is case-insensitive.




Crispin Standards Track [Page 92]

RFC 3501 IMAPv4 March 2003


 A "*" wildcard character MAY be used as the left-most name
 component in the certificate. For example, *.example.com
 would match a.example.com, foo.example.com, etc. but would
 not match example.com.

 If the certificate contains multiple names (e.g., more than
 one dNSName field), then a match with any one of the fields
 is considered acceptable.

 Both the client and server MUST check the result of the STARTTLS
 command and subsequent [TLS] negotiation to see whether acceptable
 authentication or privacy was achieved.

11.2. Other Security Considerations

 A server error message for an AUTHENTICATE command which fails due to
 invalid credentials SHOULD NOT detail why the credentials are
 invalid.

 Use of the LOGIN command sends passwords in the clear. This can be
 avoided by using the AUTHENTICATE command with a [SASL] mechanism
 that does not use plaintext passwords, by first negotiating
 encryption via STARTTLS or some other protection mechanism.

 A server implementation MUST implement a configuration that, at the
 time of authentication, requires:
 (1) The STARTTLS command has been negotiated.
 OR
 (2) Some other mechanism that protects the session from password
 snooping has been provided.
 OR
 (3) The following measures are in place:
 (a) The LOGINDISABLED capability is advertised, and [SASL]
 mechanisms (such as PLAIN) using plaintext passwords are NOT
 advertised in the CAPABILITY list.
 AND
 (b) The LOGIN command returns an error even if the password is
 correct.
 AND
 (c) The AUTHENTICATE command returns an error with all [SASL]
 mechanisms that use plaintext passwords, even if the password
 is correct.

 A server error message for a failing LOGIN command SHOULD NOT specify
 that the user name, as opposed to the password, is invalid.

 A server SHOULD have mechanisms in place to limit or delay failed
 AUTHENTICATE/LOGIN attempts.



Crispin Standards Track [Page 93]

RFC 3501 IMAPv4 March 2003


 Additional security considerations are discussed in the section
 discussing the AUTHENTICATE and LOGIN commands.

12. IANA Considerations

 IMAP4 capabilities are registered by publishing a standards track or
 IESG approved experimental RFC. The registry is currently located
 at:

 http://www.iana.org/assignments/imap4-capabilities

 As this specification revises the STARTTLS and LOGINDISABLED
 extensions previously defined in [IMAP-TLS], the registry will be
 updated accordingly.





































Crispin Standards Track [Page 94]

RFC 3501 IMAPv4 March 2003


Appendices

A. Normative References

 The following documents contain definitions or specifications that
 are necessary to understand this document properly:
 [ABNF] Crocker, D. and P. Overell, "Augmented BNF for
 Syntax Specifications: ABNF", RFC 2234,
 November 1997.

 [] Newman, C., "Anonymous SASL Mechanism", RFC
 2245, November 1997.

 [] Freed, N. and J. Postel, "IANA Character Set
 Registration Procedures", RFC 2978, October
 2000.

 [] Leach, P. and C. Newman, "Using Digest
 Authentication as a SASL Mechanism", RFC 2831,
 May 2000.

 [] Troost, R., Dorner, S. and K. Moore,
 "Communicating Presentation Information in
 Internet Messages: The Content-Disposition
 Header", RFC 2183, August 1997.

 [] Newman, C., "Using TLS with IMAP, POP3 and
 ACAP", RFC 2595, June 1999.

 [] Bradner, S., "Key words for use in RFCs to
 Indicate Requirement Levels", BCP 14, RFC 2119,
 March 1997.

 [] Alvestrand, H., "Tags for the Identification of
 Languages", BCP 47, RFC 3066, January 2001.

 [] Palme, J., Hopmann, A. and N. Shelness, "MIME
 Encapsulation of Aggregate Documents, such as
 HTML (MHTML)", RFC 2557, March 1999.

 [] Myers, J. and M. Rose, "The Content-MD5 Header
 Field", RFC 1864, October 1995.









Crispin Standards Track [Page 95]

RFC 3501 IMAPv4 March 2003


 [] Moore, K., "MIME (Multipurpose Internet Mail
 Extensions) Part Three: Message Header
 Extensions for Non-ASCII Text", RFC 2047,
 November 1996.

 [] Freed, N. and N. Borenstein, "MIME
 (Multipurpose Internet Mail Extensions) Part
 One: Format of Internet Message Bodies", RFC
 2045, November 1996.

 [] Freed, N. and N. Borenstein, "MIME
 (Multipurpose Internet Mail Extensions) Part
 Two: Media Types", RFC 2046, November 1996.

 [] Resnick, P., "Internet Message Format", RFC
 2822, April 2001.

 [] Myers, J., "Simple Authentication and Security
 Layer (SASL)", RFC 2222, October 1997.

 [] Dierks, T. and C. Allen, "The TLS Protocol
 Version 1.0", RFC 2246, January 1999.

 [] Goldsmith, D. and M. Davis, "UTF-7: A Mail-Safe
 Transformation Format of Unicode", RFC 2152,
 May 1997.

 The following documents describe quality-of-implementation issues
 that should be carefully considered when implementing this protocol:

 [] Leiba, B., "IMAP Implementation
 Recommendations", RFC 2683, September 1999.

 [] Gahrns, M., "IMAP4 Multi-Accessed Mailbox
 Practice", RFC 2180, July 1997.

A.1 Informative References

 The following documents describe related protocols:

 [] Austein, R., "Synchronization Operations for
 Disconnected IMAP4 Clients", Work in Progress.

 [] Crispin, M., "Distributed Electronic Mail
 Models in IMAP4", RFC 1733, December 1994.






Crispin Standards Track [Page 96]

RFC 3501 IMAPv4 March 2003


 [] Newman, C. and J. Myers, "ACAP -- Application
 Configuration Access Protocol", RFC 2244,
 November 1997.

 [] Klensin, J., "Simple Mail Transfer Protocol",
 STD 10, RFC 2821, April 2001.

 The following documents are historical or describe historical aspects
 of this protocol:

 [] Crispin, M., "IMAP4 Compatibility with
 IMAP2bis", RFC 2061, December 1996.

 [] Crispin, M., "IMAP4 Compatibility with IMAP2
 and IMAP2bis", RFC 1732, December 1994.

 [] Crispin, M., "Internet Message Access Protocol
 - Obsolete Syntax", RFC 2062, December 1996.

 [] Crispin, M., "Interactive Mail Access Protocol
 - Version 2", RFC 1176, August 1990.

 [] Crocker, D., "Standard for the Format of ARPA
 Internet Text Messages", STD 11, RFC 822,
 August 1982.

 [] Postel, J., "Simple Mail Transfer Protocol",
 STD 10, RFC 821, August 1982.

B. Changes from RFC 2060

 1) Clarify description of unique identifiers and their semantics.

 2) Fix the SELECT description to clarify that UIDVALIDITY is required
 in the SELECT and EXAMINE responses.

 3) Added an example of a failing search.

 4) Correct store-att-flags: "#flag" should be "1#flag".

 5) Made search and section rules clearer.

 6) Correct the STORE example.

 7) Correct "BASE645" misspelling.

 8) Remove extraneous close parenthesis in example of two-part message
 with text and BASE64 attachment.



Crispin Standards Track [Page 97]

RFC 3501 IMAPv4 March 2003


 9) Remove obsolete "MAILBOX" response from mailbox-data.

 10) A spurious "<" in the rule for mailbox-data was removed.

 11) Add CRLF to continue-req.

 12) Specifically exclude "]" from the atom in resp-text-code.

 13) Clarify that clients and servers should adhere strictly to the
 protocol syntax.

 14) Emphasize in 5.2 that EXISTS can not be used to shrink a mailbox.

 15) Add NEWNAME to resp-text-code.

 16) Clarify that the empty string, not NIL, is used as arguments to
 LIST.

 17) Clarify that NIL can be returned as a hierarchy delimiter for the
 empty string mailbox name argument if the mailbox namespace is flat.

 18) Clarify that addr-mailbox and addr-name have RFC-2822 quoting
 removed.

 19) Update UTF-7 reference.

 20) Fix example in 6.3.11.

 21) Clarify that non-existent UIDs are ignored.

 22) Update DISPOSITION reference.

 23) Expand state diagram.

 24) Clarify that partial fetch responses are only returned in
 response to a partial fetch command.

 25) Add UIDNEXT response code. Correct UIDVALIDITY definition
 reference.

 26) Further clarification of "can" vs. "MAY".

 27) Reference RFC-2119.

 28) Clarify that superfluous shifts are not permitted in modified
 UTF-7.

 29) Clarify that there are no implicit shifts in modified UTF-7.



Crispin Standards Track [Page 98]

RFC 3501 IMAPv4 March 2003


 30) Clarify that "INBOX" in a mailbox name is always INBOX, even if
 it is given as a string.

 31) Add missing open parenthesis in media-basic grammar rule.

 32) Correct attribute syntax in mailbox-data.

 33) Add UIDNEXT to EXAMINE responses.

 34) Clarify UNSEEN, PERMANENTFLAGS, UIDVALIDITY, and UIDNEXT
 responses in SELECT and EXAMINE. They are required now, but weren't
 in older versions.

 35) Update references with RFC numbers.

 36) Flush text-mime2.

 37) Clarify that modified UTF-7 names must be case-sensitive and that
 violating the convention should be avoided.

 38) Correct UID FETCH example.

 39) Clarify UID FETCH, UID STORE, and UID SEARCH vs. untagged EXPUNGE
 responses.

 40) Clarify the use of the word "convention".

 41) Clarify that a command is not "in progress" until it has been
 fully received (specifically, that a command is not "in progress"
 during command continuation negotiation).

 42) Clarify envelope defaulting.

 43) Clarify that SP means one and only one space character.

 44) Forbid silly states in LIST response.

 45) Clarify that the ENVELOPE, INTERNALDATE, RFC822*, BODY*, and UID
 for a message is static.

 46) Add BADCHARSET response code.

 47) Update formal syntax to [ABNF] conventions.

 48) Clarify trailing hierarchy delimiter in CREATE semantics.

 49) Clarify that the "blank line" is the [RFC-2822] delimiting blank
 line.



Crispin Standards Track [Page 99]

RFC 3501 IMAPv4 March 2003


 50) Clarify that RENAME should also create hierarchy as needed for
 the command to complete.

 51) Fix body-ext-mpart to not require language if disposition
 present.

 52) Clarify the RFC822.HEADER response.

 53) Correct missing space after charset astring in search.

 54) Correct missing quote for BADCHARSET in resp-text-code.

 55) Clarify that ALL, FAST, and FULL preclude any other data items
 appearing.

 56) Clarify semantics of reference argument in LIST.

 57) Clarify that a null string for SEARCH HEADER X-FOO means any
 message with a header line with a field-name of X-FOO regardless of
 the text of the header.

 58) Specifically reserve 8-bit mailbox names for future use as UTF-8.

 59) It is not an error for the client to store a flag that is not in
 the PERMANENTFLAGS list; however, the server will either ignore the
 change or make the change in the session only.

 60) Correct/clarify the text regarding superfluous shifts.

 61) Correct typographic errors in the "Changes" section.

 62) Clarify that STATUS must not be used to check for new messages in
 the selected mailbox

 63) Clarify LSUB behavior with "%" wildcard.

 64) Change AUTHORIZATION to AUTHENTICATE in section 7.5.

 65) Clarify description of multipart body type.

 66) Clarify that STORE FLAGS does not affect \Recent.

 67) Change "west" to "east" in description of timezone.

 68) Clarify that commands which break command pipelining must wait
 for a completion result response.

 69) Clarify that EXAMINE does not affect \Recent.



Crispin Standards Track [Page 100]

RFC 3501 IMAPv4 March 2003


 70) Make description of MIME structure consistent.

 71) Clarify that date searches disregard the time and timezone of the
 INTERNALDATE or Date: header. In other words, "ON 13-APR-2000" means
 messages with an INTERNALDATE text which starts with "13-APR-2000",
 even if timezone differential from the local timezone is sufficient
 to move that INTERNALDATE into the previous or next day.

 72) Clarify that the header fetches don't add a blank line if one
 isn't in the [RFC-2822] message.

 73) Clarify (in discussion of UIDs) that messages are immutable.

 74) Add an example of CHARSET searching.

 75) Clarify in SEARCH that keywords are a type of flag.

 76) Clarify the mandatory nature of the SELECT data responses.

 77) Add optional CAPABILITY response code in the initial OK or
 PREAUTH.

 78) Add note that server can send an untagged CAPABILITY command as
 part of the responses to AUTHENTICATE and LOGIN.

 79) Remove statement about it being unnecessary to issue a CAPABILITY
 command more than once in a connection. That statement is no longer
 true.

 80) Clarify that untagged EXPUNGE decrements the number of messages
 in the mailbox.

 81) Fix definition of "body" (concatenation has tighter binding than
 alternation).

 82) Add a new "Special Notes to Implementors" section with reference
 to [IMAP-IMPLEMENTATION].

 83) Clarify that an untagged CAPABILITY response to an AUTHENTICATE
 command should only be done if a security layer was not negotiated.

 84) Change the definition of atom to exclude "]". Update astring to
 include "]" for compatibility with the past. Remove resp-text-atom.

 85) Remove NEWNAME. It can't work because mailbox names can be
 literals and can include "]". Functionality can be addressed via
 referrals.




Crispin Standards Track [Page 101]

RFC 3501 IMAPv4 March 2003


 86) Move modified UTF-7 rationale in order to have more logical
 paragraph flow.

 87) Clarify UID uniqueness guarantees with the use of MUST.

 88) Note that clients should read response data until the connection
 is closed instead of immediately closing on a BYE.

 89) Change RFC-822 references to RFC-2822.

 90) Clarify that RFC-2822 should be followed instead of RFC-822.

 91) Change recommendation of optional automatic capabilities in LOGIN
 and AUTHENTICATE to use the CAPABILITY response code in the tagged
 OK. This is more interoperable than an unsolicited untagged
 CAPABILITY response.

 92) STARTTLS and AUTH=PLAIN are mandatory to implement; add
 recommendations for other [SASL] mechanisms.

 93) Clarify that a "connection" (as opposed to "server" or "command")
 is in one of the four states.

 94) Clarify that a failed or rejected command does not change state.

 95) Split references between normative and informative.

 96) Discuss authentication failure issues in security section.

 97) Clarify that a data item is not necessarily of only one data
 type.

 98) Clarify that sequence ranges are independent of order.

 99) Change an example to clarify that superfluous shifts in
 Modified-UTF7 can not be fixed just by omitting the shift. The
 entire string must be recalculated.

 100) Change Envelope Structure definition since [RFC-2822] uses
 "envelope" to refer to the [SMTP] envelope and not the envelope data
 that appears in the [RFC-2822] header.

 101) Expand on RFC822.HEADER response data vs. BODY[HEADER].

 102) Clarify Logout state semantics, change ASCII art.

 103) Security changes to comply with IESG requirements.




Crispin Standards Track [Page 102]

RFC 3501 IMAPv4 March 2003


 104) Add definition for body URI.

 105) Break sequence range definition into three rules, with rewritten
 descriptions for each.

 106) Move STARTTLS and LOGINDISABLED here from [IMAP-TLS].

 107) Add IANA Considerations section.

 108) Clarify valid client assumptions for new message UIDs vs.
 UIDNEXT.

 109) Clarify that changes to permanentflags affect concurrent
 sessions as well as subsequent sessions.

 110) Clarify that authenticated state can be entered by the CLOSE
 command.

 111) Emphasize that SELECT and EXAMINE are the exceptions to the rule
 that a failing command does not change state.

 112) Clarify that newly-appended messages have the Recent flag set.

 113) Clarify that newly-copied messages SHOULD have the Recent flag
 set.

 114) Clarify that UID commands always return the UID in FETCH
 responses.

C. Key Word Index

 +FLAGS <flag list> (store command data item) ............... 59
 +FLAGS.SILENT <flag list> (store command data item) ........ 59
 -FLAGS <flag list> (store command data item) ............... 59
 -FLAGS.SILENT <flag list> (store command data item) ........ 59
 ALERT (response code) ...................................... 64
 ALL (fetch item) ........................................... 55
 ALL (search key) ........................................... 50
 ANSWERED (search key) ...................................... 50
 APPEND (command) ........................................... 45
 AUTHENTICATE (command) ..................................... 27
 BAD (response) ............................................. 66
 BADCHARSET (response code) ................................. 64
 BCC <string> (search key) .................................. 51
 BEFORE <date> (search key) ................................. 51
 BODY (fetch item) .......................................... 55
 BODY (fetch result) ........................................ 73
 BODY <string> (search key) ................................. 51



Crispin Standards Track [Page 103]

RFC 3501 IMAPv4 March 2003


 BODY.PEEK[<section>]<<partial>> (fetch item) ............... 57
 BODYSTRUCTURE (fetch item) ................................. 57
 BODYSTRUCTURE (fetch result) ............................... 74
 BODY[<section>]<<origin octet>> (fetch result) ............. 74
 BODY[<section>]<<partial>> (fetch item) .................... 55
 BYE (response) ............................................. 67
 Body Structure (message attribute) ......................... 12
 CAPABILITY (command) ....................................... 24
 CAPABILITY (response code) ................................. 64
 CAPABILITY (response) ...................................... 68
 CC <string> (search key) ................................... 51
 CHECK (command) ............................................ 47
 CLOSE (command) ............................................ 48
 COPY (command) ............................................. 59
 CREATE (command) ........................................... 34
 DELETE (command) ........................................... 35
 DELETED (search key) ....................................... 51
 DRAFT (search key) ......................................... 51
 ENVELOPE (fetch item) ...................................... 57
 ENVELOPE (fetch result) .................................... 77
 EXAMINE (command) .......................................... 33
 EXISTS (response) .......................................... 71
 EXPUNGE (command) .......................................... 48
 EXPUNGE (response) ......................................... 72
 Envelope Structure (message attribute) ..................... 12
 FAST (fetch item) .......................................... 55
 FETCH (command) ............................................ 54
 FETCH (response) ........................................... 73
 FLAGGED (search key) ....................................... 51
 FLAGS (fetch item) ......................................... 57
 FLAGS (fetch result) ....................................... 78
 FLAGS (response) ........................................... 71
 FLAGS <flag list> (store command data item) ................ 59
 FLAGS.SILENT <flag list> (store command data item) ......... 59
 FROM <string> (search key) ................................. 51
 FULL (fetch item) .......................................... 55
 Flags (message attribute) .................................. 11
 HEADER (part specifier) .................................... 55
 HEADER <field-name> <string> (search key) .................. 51
 HEADER.FIELDS <header-list> (part specifier) ............... 55
 HEADER.FIELDS.NOT <header-list> (part specifier) ........... 55
 INTERNALDATE (fetch item) .................................. 57
 INTERNALDATE (fetch result) ................................ 78
 Internal Date (message attribute) .......................... 12
 KEYWORD <flag> (search key) ................................ 51
 Keyword (type of flag) ..................................... 11
 LARGER <n> (search key) .................................... 51
 LIST (command) ............................................. 40



Crispin Standards Track [Page 104]

RFC 3501 IMAPv4 March 2003


 LIST (response) ............................................ 69
 LOGIN (command) ............................................ 30
 LOGOUT (command) ........................................... 25
 LSUB (command) ............................................. 43
 LSUB (response) ............................................ 70
 MAY (specification requirement term) ....................... 4
 MESSAGES (status item) ..................................... 45
 MIME (part specifier) ...................................... 56
 MUST (specification requirement term) ...................... 4
 MUST NOT (specification requirement term) .................. 4
 Message Sequence Number (message attribute) ................ 10
 NEW (search key) ........................................... 51
 NO (response) .............................................. 66
 NOOP (command) ............................................. 25
 NOT <search-key> (search key) .............................. 52
 OK (response) .............................................. 65
 OLD (search key) ........................................... 52
 ON <date> (search key) ..................................... 52
 OPTIONAL (specification requirement term) .................. 4
 OR <search-key1> <search-key2> (search key) ................ 52
 PARSE (response code) ...................................... 64
 PERMANENTFLAGS (response code) ............................. 64
 PREAUTH (response) ......................................... 67
 Permanent Flag (class of flag) ............................. 12
 READ-ONLY (response code) .................................. 65
 READ-WRITE (response code) ................................. 65
 RECENT (response) .......................................... 72
 RECENT (search key) ........................................ 52
 RECENT (status item) ....................................... 45
 RENAME (command) ........................................... 37
 REQUIRED (specification requirement term) .................. 4
 RFC822 (fetch item) ........................................ 57
 RFC822 (fetch result) ...................................... 78
 RFC822.HEADER (fetch item) ................................. 57
 RFC822.HEADER (fetch result) ............................... 78
 RFC822.SIZE (fetch item) ................................... 57
 RFC822.SIZE (fetch result) ................................. 78
 RFC822.TEXT (fetch item) ................................... 58
 RFC822.TEXT (fetch result) ................................. 79
 SEARCH (command) ........................................... 49
 SEARCH (response) .......................................... 71
 SEEN (search key) .......................................... 52
 SELECT (command) ........................................... 31
 SENTBEFORE <date> (search key) ............................. 52
 SENTON <date> (search key) ................................. 52
 SENTSINCE <date> (search key) .............................. 52
 SHOULD (specification requirement term) .................... 4
 SHOULD NOT (specification requirement term) ................ 4



Crispin Standards Track [Page 105]

RFC 3501 IMAPv4 March 2003


 SINCE <date> (search key) .................................. 52
 SMALLER <n> (search key) ................................... 52
 STARTTLS (command) ......................................... 27
 STATUS (command) ........................................... 44
 STATUS (response) .......................................... 70
 STORE (command) ............................................ 58
 SUBJECT <string> (search key) .............................. 53
 SUBSCRIBE (command) ........................................ 38
 Session Flag (class of flag) ............................... 12
 System Flag (type of flag) ................................. 11
 TEXT (part specifier) ...................................... 56
 TEXT <string> (search key) ................................. 53
 TO <string> (search key) ................................... 53
 TRYCREATE (response code) .................................. 65
 UID (command) .............................................. 60
 UID (fetch item) ........................................... 58
 UID (fetch result) ......................................... 79
 UID <sequence set> (search key) ............................ 53
 UIDNEXT (response code) .................................... 65
 UIDNEXT (status item) ...................................... 45
 UIDVALIDITY (response code) ................................ 65
 UIDVALIDITY (status item) .................................. 45
 UNANSWERED (search key) .................................... 53
 UNDELETED (search key) ..................................... 53
 UNDRAFT (search key) ....................................... 53
 UNFLAGGED (search key) ..................................... 53
 UNKEYWORD <flag> (search key) .............................. 53
 UNSEEN (response code) ..................................... 65
 UNSEEN (search key) ........................................ 53
 UNSEEN (status item) ....................................... 45
 UNSUBSCRIBE (command) ...................................... 39
 Unique Identifier (UID) (message attribute) ................ 8
 X<atom> (command) .......................................... 62
 [RFC-2822] Size (message attribute) ........................ 12
 \Answered (system flag) .................................... 11
 \Deleted (system flag) ..................................... 11
 \Draft (system flag) ....................................... 11
 \Flagged (system flag) ..................................... 11
 \Marked (mailbox name attribute) ........................... 69
 \Noinferiors (mailbox name attribute) ...................... 69
 \Noselect (mailbox name attribute) ......................... 69
 \Recent (system flag) ...................................... 11
 \Seen (system flag) ........................................ 11
 \Unmarked (mailbox name attribute) ......................... 69







Crispin Standards Track [Page 106]

RFC 3501 IMAPv4 March 2003


Author's Address

 Mark R. Crispin
 Networks and Distributed Computing
 University of Washington
 4545 15th Avenue NE
 Seattle, WA 98105-4527

 Phone: (206) 543-5762

 EMail: MRC@CAC.Washington.EDU








































Crispin Standards Track [Page 107]

RFC 3501 IMAPv4 March 2003


Full Copyright Statement

 Copyright (C) The Internet Society (2003). All Rights Reserved.

 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works. However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.

 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns. v This
 document and the information contained herein is provided on an "AS
 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
 FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
 LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
 NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
 OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.




















Crispin Standards Track [Page 108]