Leave Message on Server for x Days - Not Working

I have a client who is all POP3 and one user wants to leave the messages on the server for about 10 days because he has a Treo which also checks POP3. The reason being if he leaves Outlook open at work by accident he doesn't want to lose the Treo's ability.

However it is not deleting messages at all. I confirmed he does, in fact, have the appropriate box checked and the number 10 in the appropriate field. I was noticing a large increase in this client's overall disk utilization thus found emails in the one user's email box back to 4/1. I since deleted them up to 10 days back but still no go. I really do not think this is an Outlook issue at this point.

Any help would be appreciated.

Thanks