To encrypt email in Outlook, you can use either S/MIME encryption or Microsoft Purview Message Encryption (also known as Microsoft 365 Message Encryption). Here is how to do it:

Encrypt a Single Email Message in Outlook

1. Compose a new email message.
2. In the message window, go to the Options tab.
3. Click Encrypt.
4. Choose the encryption option you want, such as Encrypt or Do Not Forward (which prevents recipients from forwarding the email).
5. Finish composing your email and send it.

This works in both the new Outlook and classic Outlook versions

Encrypt All Outgoing Messages Using S/MIME (Classic Outlook)

1. Go to File > Options > Trust Center > Trust Center Settings.
2. Select the Email Security tab.
3. Under Encrypted email , check Encrypt contents and attachments for outgoing messages.
4. Optionally, click Settings to choose a specific certificate for encryption.
5. Click OK to save.

Note that all recipients must have your digital ID (certificate) to decrypt your emails

Setup Requirements for S/MIME Encryption

• You must obtain an email encryption certificate (digital ID) from a trusted Certificate Authority (e.g., Comodo, GlobalSign, IdenTrust).
• Import the certificate into Outlook via File > Options > Trust Center > Trust Center Settings > Email Security > Import/Export.
• Share your public key (digital signature) with recipients by sending them a digitally signed email.
• Recipients need your public key to send you encrypted emails, and you need their certificates to send encrypted emails to them

Using Microsoft Purview Message Encryption (Microsoft 365)

• Available if your email server has an Office 365 Enterprise E3 license.
• In a new email, select Options > Encrypt , then choose the desired restrictions.
• This encryption does not require exchanging certificates but requires proper licensing.
• Avoid mixing S/MIME and Purview encryption on the same message

Summary

Method| How to Use| Requirements
---|---|---
S/MIME Single Message| Options > Encrypt > Choose option > Send| Digital certificate, recipient cert
S/MIME All Outgoing Messages| File > Options > Trust Center > Email Security > Encrypt all outgoing| Digital certificate, recipient cert
Microsoft Purview Encryption| Options > Encrypt > Choose option > Send| Office 365 Enterprise E3 license

This approach ensures your emails are encrypted and protected from unauthorized access during transmission