Outlook 2002 doe not deliver, shows messages being sent...

[Lloyd Alexander]

I intermittently get the following when trying to send out
messages: "The recipient was unavailable to take delivery
of the message" with a reference to our domain ending
with "3499 Host unreachable".

I've looked everywhere for help but cannot find anything.

I installed SP1 for Outlook 2002, no luck.

Note: it is NOT consistent. Sometimes things actually get
sent.