I asked this question a few weeks back. I haven't found a solution yet, so I thought I'd ask again...
I have a client with an SBS2003 server and 3 client laptops that connect via a wireless lan when they are in the office, and by Outlook via the Internet when outside the office.
Two of the users have a problem. Occasionally when they send an email, it sticks in the Outbox and doesn't send. This happens both inside the office and when they are off site. When a message is stuck in the Outbox, they can compose and send another message which will send normally. They can also Forward the stuck message, and the forwarded message will send normally. Eventually the stuck messages will get sent. It seems strange that other messages can be sent and received normally while there is a message stuck in the Outbox. I have asked them to check for Internet connectivity at the time a message is stuck. They always report that Internet connectivity is normal.
This has been happening ever since I installed the server 6 weeks ago. I am getting pressure put on me to resolve this now.