Outlook email inbox items disappearing from both 2003 and 2007

I have a user who’s email inbox items are disappearing. They are there for a certain amount of time then gone. It happens in both Outlook 2003/07, Vista or XP, different workstations. He can go into tools/recover deleted items and restore them back. He has NO rules setup. We did a Front end server hardware upgrade the night before and I’m assuming it should make no difference except for coincidence. Could there be something created server side that is causing this. All other users are fine.