Cannot send but can reply
 

I recently installed SBS 2003 on peer-to-peer network (all Win XP Pro
clients) and configured Exchange server for all outlook email. Sending email
is through exchange connector to ISP SMTP. Unfortunately, I am having
trouble sending newly created emails and forwarding emails. Strangely, I can
successfully reply.

Symptoms are as follows:
1. I send a new email.
2. Email appears to successfully send with the message being saved in the
SENT folder.
3. About a day later I get a message from the "Administrator" saying
Subj: Delivery Status Notification (Delay)
....
THIS IS A WARNING MESSAGE ONLY
Delivery to the following recipients has been delayed:

4. about a day later I get another message from the "System Administrator"
saying
subj: UNDELIVERABLE 'email subject'
Your message did not reach some or all of the intended recipients.
Subj: yada yada
Date: anytime
The following recipients could not be reached:

Could not deliver the message in the time limit specified. Please retry or
contact your administrator. mydomain.net #4.4.7

Anyone have any ideas what the problem could be?
--
Thanks,
KP