A company deploys a system to use device and user certificates form network authentication. Previously, the company only used separate certificates to send/receive encrypted email. Users have begun notifying the help because they cannot read encrypted email. Which of the following is the MOST likely cause of the issues?

A. The attestation services is no configured to accept the new certificates

B. The device certificates have the S/MIME attribute selected

C. The sending mal client is selecting the wrong public key to encrypt message

D. Multiple device certificates are associated with the same network port