Missing Emails In OE6

Help!! One of our employees came to me today saying that a large majority of his emails had vanished from folders in his inbox. My first thoughts were that he had accidently deleted them and they would be in his deleted items, they weren?t. I have no idea where they may be or what he has done, I would appreciate any help! He is using OE6 and downloading his mail from a Unix Server, which does not save copies of mail and he hasn?t backed up his machine in a long time!