I replied a message to a user but he did not get it but when I used the Trace utility on my Exchange 2007, I can see it was sent and delivered. My user tried click on "Send and Receive" couple times or using OWA to check it, still no luck.
However; when I send him a regular email (not reply), he can get it. He can get some of my reply, not all of them.
I am using Ex2K7 SP1.
I am attaching my snapshot of trace log from Ex2K7.