How to verify missing emails?

[bhwong]

Is it possible that an email sending to 6 of our users where all of them have received it except one? If so, what could be the possible cause?

Some of our users often claims that Zimbra failed to send and receive emails. How can I verify this since they might intentionally delete those emails to claim innocence of not doing their work since they have never receive any work instruction from their emails?

Which log files can I check to verify this? Is there any verification we can do from our side? Such as creating a shadow account to match with their incoming and outgoing emails etc?

[lytledd]

If it happens often enough, you should be able to see it in one or more logs:

/var/log/mail.log
/var/log/zimbra.log
/opt/zimbra/log/mailbox.log

Doug