A financial analyst is expecting an email containing sensitive information from a client.

The most likely cause of the issue is that the S/MIME plug-in is not enabled. S/MIME stands for Secure/Multipurpose Internet Mail Extensions, which is a standard that allows email users to encrypt and digitally sign their messages. S/MIME uses public key cryptography and certificates to ensure confidentiality, integrity, authenticity, and non-repudiation of email communications. However, S/MIME requires both the sender and the receiver to have compatible email clients and plug-ins that support S/MIME functionality. If the receiver does not have the S/MIME plug-in enabled, they will not be able to decrypt or verify the encrypted message.