Exchange 2003 server account problems?

I have an account that cannot receive emails. I am using the Exchange 2003 server. I have tried setting up the Exchange user on 3 computers and every time you pull more than half of your emails, and they hang on a certain percentage.
As of now it’s stuck at 57%, however, it hangs at a different percentage each time. Obviously not a matter of perspective, I’ve used Outlook 2003 and 2007 in 3 different computers, so it should be an issue of exchange / mailbox.
Any ideas on how i should solve this problem?
