Secure messages with a digital signature

By digitally signing a message, you apply your unique digital mark to the message. The digital signature includes your certificate and public key. This information proves to the recipient that you signed the contents of the message and not an imposter, and that the contents have not been altered in transit. For additional privacy, you can also encrypt messages.


  • Digitally signing a message is not the same as including a signature in outgoing messages. Anyone can copy an e-mail signature, which is essentially a customizable closing salutation. By contrast, a digitally signed message can come only from the owner of the digital ID used to sign it. This provides verification of the sender's authenticity, thereby helping prevent message tampering.

  • You may want to learn more about digital signatures.

In this article

Digitally sign an individual message

Digitally sign all messages

Digitally sign an individual message

  1. In the message, on the Message tab, in the Options group, click the Digitally Sign Message button Button image .

    Note: If you don't see this button, click the Options Dialog Box Launcher in the lower right corner of the Optionsgroup to open the Message Options dialog box. Click the Security Settings button and in the Security Properties dialog box, select Add digital signature to this message. Click OK and then close the Message Options dialog box.

  2. Compose your message and send it.

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Digitally sign all messages

  1. On the Tools menu on the Outlook Mail view, click Trust Center to open the Trust Center dialog box, and at the far left of the dialog box, click E-mail Security.

  2. Under Encrypted e-mail, select the Add digital signature to outgoing messages check box.

  3. 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. This check box is selected by default.

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

  4. To change additional settings, such as choosing a specific certificate to use, click Settings.

  5. Click OK twice.

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