Sierra 10.12.2 S/MIME Email Address Mismatch

Hi,

Since the update to 10.12.2 we have lost the ability to S/MIME encrypt messages to our customer contacts using Mac OS Mail.

Customer email addresses that previously would enable encrypted email using the customer's validated and trusted certificates view-able in Keychain Access will no longer encrypt.

If I "Evaluate" any of the customer S/MIME certificates using the Keychain Access application both the Evaluation Status and the Certificate Status now come back as "S/MIME Email address mismatch"

The customer certificates have not changed and are the same certificates that previously all worked prior to 10.12.2.

The S/MIME email encryption with the same customer certificates works perfectly on our iPhones (iOS 10.2).

The customer has thousands of employees with S/MIME certificates and there is no email encryption problem when corresponding with Window's based machines.

Is there a way to work around this "Mismatch" issue in Sierra 10.12.2?

Is this a bug in Mac OS Sierra 10.12.2?

Does my company need to change our email application to Outlook or some other platform that will support S/MIME encryption on our desktop Mac OS machines?

Any help with this would be appreciated.

Thanks

Vince