A digital signature attached to an email message offers another layer of security by providing assurance to the recipient that you—not an imposter—signed the contents of the email message. Your digital signature, which includes your certificate and public key, originates from your digital ID. And that digital ID serves as your unique digital mark and signals the recipient that the content hasn’t been altered in transit. For additional privacy, you also can encrypt email messages.

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 Permission group, click Sign Message.
    • If you don’t see the Sign Message button, do the following:
      • In the message, click Options.
      • In the More Options group, click the dialog box launcher Dialog Box Launcher button on the ribbon in the lower-right corner.
      • Click Security Settings, and then select the Add digital signature to this message check box.
      • Click OK, and then click 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, click Options > Trust Center.
      • Under Microsoft Outlook Trust Center, click Trust Center Settings > Email Security
      • Click Import/Export to import a digital ID from a file on your computer, or click Get digital IDs to find a list of services that issue digital IDs for your use.
  2. Compose your message, and then send it.

Digitally sign all messages

  1. On the File tab, click Options >Trust Center.
  2. Under Microsoft Outlook Trust Center, click 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, click Settings.
  6. Click OK on each open dialog box.