Outbox will not clear

Hello,

A friend of mine called me last night from Florida and he had a really weird email problem. He has Outlook Express with no virii and all of the updates. When he sends an email, it stays in the Outbox and never clears. While this is going on I am getting that message repeatedly like every second or so. So the email won’t go away and his screen still shows the sending bar…because it is like mass mailing that one email. Now when he goes on to his son’s OE account he sends one email fine. What is the problem here? If anyone can help, it would be greatly appreciated.

Thank you again