DUH! Turns out our settings were not entirely correct.
Here's what was causing the problem. If you go to
properties of the Default SMTP Virtual server->Delivery
tab->Advanced, a smart host was defined that was carried
over from the 5.5 upgrade. At that time it was needed,
but after changing ISP's, the smart host was no longer
valid or needed.
>We are receiving the error referenced in the subject
>field. A description is below.
>Intermittently, I receive back to my server undeliverable
>emails. They are returned for relaying errors. The
>text of the returned failure is below.
> Your message did not reach some or all of the intended
> Subject: RE: how do i get some anti-freeze
> Sent: 11/25/2002 8:59 AM
>The following recipient(s) could not be reached:
> 'Christine Cohen' on 11/25/2002 9:01 AM
> There was a SMTP communication problem with
>the recipient's email server. Please contact your system
> <hercules.hcci.net #5.5.0 smtp;550 Relaying
>This happens to different users sending to different
>domains. If the user resends the message, it goes
>through. The Exchange server is running sp2, all users
>are on the same subnet as the server and we have
>that the server is configured correctly to only allow
>relays from the local net.