OS X Lion: Mail doesn't send certificate-signed message; Compose window cannot be closed

When attempting to send a message in Mail that has been signed by a trusted certificate, a message may briefly appear that states:

"Unable to sign message
You don’t have a trusted certificate in your keychain that matches the email address (sender’s email address). Without a certificate, you can’t sign messages sent from this address."


The message quickly disappears, and the Compose window reappears but cannot be closed.

This message indicates that your keychain contains an invalid certificate for the sender’s email address.

  1. Quit Mail if it's open.
  2. Open Keychain Access, located in the Utilities folder, in the Applications folder. 
  3. Click the “Login” keychain in the left column. 
  4. Locate the certificate with the same name as the email address displayed in the message that appeared when the email did not send. 
  5. Remove the certificate from the keychain by pressing the Delete key. 
  6. Open Mail.
  7. Attempt to send the email message again.


Note: This issue doesn't occur with Mail messages that have signatures, such as your name.

Learn more

What is a “signed message”?

If you have a personal certificate on your computer, you can send secure signed messages (including the body of the message and any attachments) to anyone using Mail. A personal certificate is an electronic document that associates your digital identity with other information, such as your name or email address. If you want to send and receive signed and encrypted messages, you need a personal certificate.

 

Signed messages let your recipients verify your identity as the sender, and provide assurance that the message has not been tampered with in transit. A Signed icon (a checkmark) in the email header indicates your personal certificate is installed in Keychain Access.

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