This article covers the different methods to encrypt email messages in Outlook: using certificates (S/Mime), Office 365 Message Encryption (OME), and using encryption add-ins.
To Encrypt a single message:
1. In message that you are composing, click File > Properties.
2. Click Security Settings, and then select the Encrypt message contents and attachments check box.
3. Compose your message, and then click Send.
In Outlook, All attachments are encrypted.
Recipients who access the encrypted email via the Office Message Encryption portal can view attachments in the browser.
Note that if the recipient of the file is using an Outlook.com account, they can open encrypted Office attachments on the Office apps for Windows.
To view an encrypted email in Outlook:
1. Select Read the message.
2. You'll be redirected to a page where you can sign in and receive a single-use code.
3. Check your email for the single-use code. Enter the code in the browser window, then select Continue to read your message.
To encrypt a message in Office 365:
1. Sign in with Global Admin credentials.
2. Click on Admin.
3. Click on Settings.
4. Click on Services & add-ins.
5. Click on Microsoft Azure Information Protection.