How to Send a Secure Email in Outlook

This guide shows you how to send a secure email in Outlook using the desktop version of Microsoft Outlook with a Microsoft 365 account. You'll configure S/MIME encryption in the Trust Center and then apply it to a new message before sending.

Prerequisites

• You need Microsoft Outlook (desktop version) connected to a Microsoft 365 account.
• Your recipient must also use Outlook 365. Both sender and recipient need Outlook 365 for encrypted messages to work correctly.

Configuring the settings for an encrypted email

Before you can send a secure email in Outlook, you need to set up your encryption preferences in the Trust Center.

1. Open File in the top-left corner of Outlook.
2. Select Options to open the Outlook Options dialog.
3. In the left sidebar, select Trust Center.

4. Click Trust Center Settings to open the Trust Center dialog.

5. In the Trust Center dialog, select Email Security from the left sidebar.

6. Under the "Encrypted email" section, click Settings....

7. In the Change Security Settings dialog, configure the following:

   • Enter a name in the Security Settings Name field (for example, "MEO").
   • Set Cryptography Format to S/MIME.
   • Confirm or select your Signing Certificate and Encryption Certificate (for example, "Microsoft Your Phone").
   • Set Hash Algorithm to SHA1.
   • Set Encryption Algorithm to AES (256-bit).
   • Make sure the checkbox for "Send these certificates with signed messages" is checked.
8. Click OK to save your settings.

9. Back in the Trust Center dialog, confirm that your new setting (for example, "MEO") now appears under Default Setting.
10. Click OK to close the Trust Center dialog, then click OK again to close the Outlook Options dialog.

With these settings saved, Outlook is now configured to send encrypted emails using your chosen security settings.

Writing and sending a secure email in Outlook

1. Return to the main Outlook window and click New Email to open a new message.

2. In the new message window, go to the Options tab on the ribbon.

3. Under the Encrypt section, click the Encrypt button to open the encryption options dropdown.

4. Select Encrypt with S/MIME from the dropdown menu. A tooltip may appear stating "Encrypt this message using S/MIME."

5. Confirm that the Encrypt button is now highlighted, which indicates encryption is enabled for this message.
6. Compose your email as usual. It will be sent encrypted.

What's next

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Summary

By following these steps, you've configured Outlook's Trust Center settings and learned how to send a secure email in Outlook using S/MIME encryption. Once your security settings are saved as the default, you can apply encryption to any new message from the Options tab before sending.