The workaround is to not look in the outbox unless you need to edit something before it sends. In fact that method is likely why it works that way.
Bob
I run Win XP SP2 and have recently installed Office 2003. I have a problem sending mail.
If a message is selected (highlighted) in the outbox (by a left-click with the mouse or with the arrow keys on the keyboard), its icon changes to edit-mode and the date in the Sent- column changes to "none". Only this selected message will not be sent during a send/receive, all other messages in the outbox are. If there is only one message in the outbox, it's automatically selected and this prevents it from being sent during a send/receive. Clicking somewhere else in the space under the messages in the outbox doesn't deselect the message.
To work-around the problem I deselect the message (by pressing the Ctrl key while selecting the message). To resend it I have to open it again without highlighting the message (with a rightclick on the message and select open from the menu). After re-sending the message it is placed in the outbox correctly (not selected and with a send date and the right icon)and I can finally send it.
Any other solutions to fix this problem? I already tried uninstalling and reinstalling outlook.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic