Disappearing email

[14643rusty]

I'm running ZCS 8.0.8 on Ubuntu 10.04. I have one user who has occasional incoming emails show up in his inbox for 1-2 seconds and disappear. He notices this when at his computer in the office using outlook. After looking at his office computer, I am thinking it is anti-virus or anti-spam on one of his other computers at home or another location that is causing this behavior. He has 5 or 6 devices connected to this Zimbra account.
I don't know that I can depend on him to help troubleshoot which device is removing said emails. Is there a way I can determine which computer is at fault from the logs?
It's not a rule or filter.

[Gren Elliot]

You could turn on tracing for SOAP, IMAP and POP3 perhaps.
e.g.
zmprov addAccountLogger user1@example.com zimbra.soap trace
zmprov addAccountLogger user1@example.com zimbra.imap trace
zmprov addAccountLogger user1@example.com zimbra.pop trace

Then see if there are any obvious attempts to delete incoming messages from those types of clients.