Hello,
- What version of BES?
- Do any other users complain of the same issues?
- Is there anything inherently different with his Exchange account than your other BES users?
- Is he in a different location than normal?
- Do the messages eventually deliver or do they remain in a pending state? If they deliver, is it a result of troubleshooting you have done (battery pull, resending service books, etc.)
I would try putting him on a static messaging agent to see if this helps:
KB12766-How to assign a BlackBerry smartphone user to a static mailbox agent on a BlackBerry Enterprise Server