Composed messages sit in the outbox

The problem is I have some users that compose new
messages and when they click on send, the email will
remain in the outbox until they click on a different
folder.

The same users are experiencing a delay in receiving
emails. If Outlook sits idle, the user will click on
Inbox and then they will receive several emails, most of
which were sent 10-15 minutes ago and as long as 1 hour
ago.

The Send/Receive configuration has not been changed from
the default values. We are not scheduling send/receive
every X minutes. The Send/Receive button doesn't seem to
work.

Outlook 2000 SP3
XP Pro

Thanks,
Sean