outlook 2003, xp sp2, all updates, 5 computers total. All of them
throughout the day have all kinds of trouble sending out emails. after
the users click send, they are moved to the outbox where they remain
for sometimes 10-15-20 minutes, half the time they never send at all.
other times I have to close outlook, restart, send/receive, and they
send. if that doesn't work, sometimes i can go to the outbox, double
click the messages, and hit 'send' again and they will leave the
outbox and send successfully.

we don't have any of these plugins installed; http://www.slipstick.com/problems/outbox.htm

these are all vanilla outlook 2k3 installs. Why is this happening?