email failure in hosted domain

In one of my domains hosted on a VM Pro box (CentOS), the user is not receiving email from any @smithbarney addresses. I had him send an email from his @smithbarney account to both my account on the VM server and another account on a different server. The message came through on the other server, but not even a log entry on teh VM Pro box. Other mail from external sources comes in just fine on the VM Pro box.

Any clue on selective email rejection with no logfile entry?