We have a notebook user that has had repeated issues with messages jamming in their Outbox when they are working from remote. To fix the problem the user moves the message to the Draft Folder, deletes the message in the Outbox and then opens and resends.
The problem appears to be triggered when the user has opened the new mail dialog box to compose a message and then left it open for a long period time, to compose the message, etc. Sometimes the user gets side tracked and then finishes and sends the message.
In addition, he can receive new messages, but any message he sends after the one gets jammed just continues to build. He has to move them all to the Draft folder, and then resend each.