I have been moving from Google and Microsoft to Proton products. Proton's email and other products include encryption by default, and password-protecting messages adds a layer of security. However, I still need to use the Outlook app on Windows 11 since I haven’t completely transferred all my accounts yet. I also need to use it in various work environments throughout the day. Sometimes, I need to send sensitive information, and it’s less convenient to use Proton. Also, on the rare occasion I work from a Mac, the process is the same with a 365 account.

Since using Proton, I’ve taken encryption for granted. Luckily, Outlook makes it possible to encrypt an email message. Since I have a Microsoft 365 account, I can use the encryption feature to protect the privacy and security of my messages. This also includes attachments; if you have sensitive documents, there are good reasons to encrypt the message.

4 Extra security layers

Protect your email from your device to Microsoft servers

Outlook uses various security layers, like Transport Layer Security (TLS), to encrypt your email’s content while in transit. Large email providers like Gmail, Yahoo, and Proton support this protocol. Outlook also uses Secure/Multipurpose Internet Mail Extensions (S/MIME) and its own Purview Message Encryption for the content of your message. The latter ensures the content of your message is encrypted while sitting in your inbox. So I can have peace of mind knowing my messages are private and secure.

If an unauthorized user were to gain access to your email, the message content would be scrambled with random characters. Only the allowed and intended recipient with the correct decryption key can read its content. Sending messages to existing Outlook (or Microsoft 365) users makes viewing the message easier for the recipient since it’s within the same system.

3 Secure email communication

It’s private and secure

Since Outlook uses multiple layers of encryption, including S/MIME and TLS, I know that my encrypted email communications are secure. I can send messages with sensitive information securely. Knowing it is safe from hackers, malicious code, and bad actors. For instance, I email my tax accountant, doctor, and credit card companies, as well as any other entities I want to ensure are confidential and protected.

I also encrypt messages in Outlook to send contracts, software codes, and embargoed announcements from tech companies I write about. It’s essential to note that encryption can be removed before sending the email, but it cannot be removed after it has been sent. So, if I do that, I typically resend the message so it’s easier on the recipient.

2 Adding encryption is straightforward

It only takes a few steps to encrypt email messages in the Outlook app

Encrypting your email in the Outlook app (or web) is straightforward from the controls on the ribbon. Compose your message and add any attachments. Click the Options tab, select the Encrypt button, and send the email. The recipient can read the encrypted message if they are in the Microsoft 365 ecosystem. If the recipient uses the Outlook app (Windows or Mac), Outlook on the web, or the mobile app on an iPhone or Android device and has signed in with their account, no action is required. They will be able to read the message like unencrypted emails.

However, it is worth noting that they will see a message indicating that it is an encrypted email. A lock icon will also appear next to the message in their inbox. If the recipient is on another service like Gmail, the message will say it’s encrypted with a link to Outlook on the web. They can sign in with their Microsoft account (if they have one) or use a one-time password to access the email, including attachments.

1 There is another security feature

The Do Not Forward option differs from the encrypt option

In addition to encrypting your emails while at rest and in transit, Outlook includes an additional security feature called Do Not Forward. The message stays encrypted within the Microsoft 365 architecture when you choose this feature. It cannot be copied or forwarded. Also, the attachments remain encrypted after downloading. If the recipient emails the attachment to someone else, the file will not open for them. The recipient can open files if they are running Microsoft 365 apps. But PDFs and media files (.mp3, .JPG, .PNG, etc.) can be downloaded.

Enabling this feature is similar. Compose your message and add any attachments. Go to Options -> Encrypt -> Do Not Forward. Outlook will indicate that the message is encrypted and cannot be forwarded. Click Send.

Encrypting your email in the Outlook app for security

If you need to keep sensitive data secure, using the Outlook app is a straightforward process. It’s just a matter of composing your message and clicking a few buttons. It’s unlikely you need to encrypt all your messages for personal use. However, when you need to send sensitive messages and documents, you will want to use the security feature to ensure their security. It’s also easy for the recipient if they are also in the Microsoft 365 ecosystem. However, they can still obtain a one-time password to view it, even if they aren't.

It’s worth noting that if you use an email service like Proton, messages aren’t encrypted in the same way. For example, Proton uses TLS to encrypt email while in transit. However, unless you password-protect your message, it is not end-to-end encrypted. This ensures better compatibility with services that support TLS, such as Gmail, Yahoo, or Outlook. However, if a message is password-protected, the encryption acts like Outlook’s encryption feature. Ultimately, to encrypt emails with attachments, a few extra steps are required when using either service.