Secure messages by using a digital signature in Outlook

What's the difference between a digital signature and a standard signature?

A digital signature isn't the same as a signature you routinely include with an outgoing message. Anyone can copy an email signature, which essentially is a customizable closing salutation. But a digitally signed message can come only from the owner of the digital ID used to sign it. The digital ID provides verification of the sender's authenticity, thereby helping to prevent message tampering.

You can learn more about digital signatures and how to get a digital ID.

Digitally sign a single message

1. In the message, on the Options tab, in the Encrypt group, select Sign.

   • If you don't see the Sign Message button, do the following:

     • In the message, select Options.

     • In the More Options group, select the dialog box launcher in the lower-right corner.

     • Select Security Settings, and then select the Add digital signature to this message check box.

     • Select OK, and then select Close.

   • If you don't see the Sign Message button, you might not have a digital ID configured to digitally sign messages, and you need to do the following to install a digital signature.

     • On the File menu, select Options > Trust Center.

     • Under Microsoft Outlook Trust Center, select Trust Center Settings > Email Security

     • Select Import/Export to import a digital ID from a file on your computer.

2. Compose your message, and then send it.

Digitally sign all messages

1. On the File tab, select Options >Trust Center.

2. Under Microsoft Outlook Trust Center, select Trust Center Settings.

3. On the Email Security tab, under Encrypted Mail, select the Add digital signature to outgoing messages check box.

4. If available, you can select one of the following options:

   • If you want recipients who don't have S/MIME security to be able to read the message, select the Send clear text signed message when sending signed messages check box. By default, this check box is selected.

   • To verify that your digitally signed message was received unaltered by the intended recipients, select the Request S/MIME receipt for all S/MIME signed messages check box. You can request notification telling you who opened the message and when it was opened, When you send a message that uses an S/MIME return receipt request, this verification information is returned as a message sent to your Inbox.

5. To change additional settings, such as choosing between multiple certificates to use, select Settings.

6. Select OK on each open dialog box.

See also

Send encrypted email messages in Outlook

View and reply to encrypted messages in Outlook

​​​​​​​Get a digital ID

Find digital ID or digital ID services

Send a digitally signed or encrypted message for Mac

Advanced Outlook.com security for Microsoft 365 subscribers

Learn about encrypted messages in Outlook.com

Encrypt messages using S/MIME in Outlook on the web