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When someone checks your driver's license or other photo ID to make sure that you are who you say you are, it is important that they check to match your photo with your face. Similarly, when you get a message in Microsoft Office Outlook 2007 containing a digital signature (digital signature: An electronic, encryption-based, secure stamp of authentication on a macro or document. This signature confirms that the macro or document originated from the signer and has not been altered.), it is important to make sure that the signer is who you think the person is. Use the following procedure to verify someone's digital signature.

 Note   You may find it helpful to read about digital signatures, and about how to digitally sign an e-mail message.

1. Open the digitally signed message.
2. Look at the Signed By status line to check the e-mail address of the person who signed the message. It is not enough to check the e-mail address in the From line because you want to verify who actually signed the message, not just who sent the message.

   

    Important   If the e-mail address in the From line does not match the e-mail address in the Signed By status line, the Signed by line is the one you should go by to determine who actually sent the message.

   

3. Check to see whether the signature is valid or invalid.
   • If the button on the Signed By status line appears similar to the following Signature button , the signature is valid. For more information about the status of the signature, click the button.
   • If a red underline appears under the Signed By status line and if the button appears as an exclamation mark, the signature is invalid. For more information about the status of the signature, click the button.

     

4. To see more information about why there is a problem with the digital signature, such as the certificate being invalid, click Details.

   

5. In the next security dialog box that appears, click View Details to see information about the certificate used in the digital signature.

  Notes  

• There can be several reasons for why the digital signature is not valid. For example, the sender's certificate (certificate: A digital means of proving your identity. When you send a digitally signed message you are sending your certificate and public key. Certificates are issued by a certification authority, and like a driver's license, can expire or be revoked.) may have expired, it may have been revoked by the certificate authority (CA) (certificate authority (CA): An entity, similar to a notary public, that issues digital certificates, keeps track of who is assigned to a certificate, signs certificates to verify their validity, and tracks which certificates are revoked or expired.), or the server that verifies the certificate may be unavailable. Contact the sender and notify them of the problem.
• If a delegate (delegate: Someone granted permission to open another person's folders, create items, and respond to requests for that person. The person granting delegate permission determines the folders the delegate can access and the changes the delegate can make.) sent the message on behalf of another person, then the delegate's name appears as the sender.