S/MIME Signature Encryption Issues


This article lists common issues when working with S/MIME Email Encryption and potential resolutions.

Note: Please visit the Email Encryption service page for more information on email encryption.


Cannot Encrypt with S/MIME

The following error may occur when attempting to send encrypted emails from Outlook:

  • "A custom mail flow rule created by an admin at utdallas.edu has blocked your message. Cannot encrypt with SMIME Signature. Please remove SMIME Signature."

This error will be presented if you sign an email destined for an external recipient (outside UTD) with a digital certificate and attempt to encrypt the email with the "[encrypt]" phrase in the subject line. Because the recipient is external to UTD, the encryption will fail, and the message will not be delivered.

You must remove the S/MIME digital signature from your email before sending it to an external recipient with the "[encrypt]" tag. For more information on sending encrypted emails, please visit this article.

For further assistance, please contact the OIT Helpdesk.


Article ID: 455
Mon 11/22/21 12:56 PM
Thu 8/31/23 9:24 PM

Related Services / Offerings (1)

Email Encryption allows users to send encrypted emails to people inside or outside the organization. To view encrypted messages, recipients will receive a one-time passcode (guests), or UTD students, staff, and faculty can log in with their UTD credentials.