iis smtp nntp: Windows 2003 SP1
IIS 6

I have 1 IIS server in a DMZ that passes incoming mail to my internal
network.

For months I have been able to accept email addressed to user@abc.com.
I now must accept mail addressed to user@xyz.ca.

MX and A records have been setup and resolve correctly (tested from
dnsstuff).

A remote domain for xyz.ca was setup in the IIS SMTP VS. It was configured
identically to abc.com.

Mail addressed to abc.com still arrives flawlessly, but mail addressed to
xyz.ca is always rejected with error "550 5.7.1 Unable to relay for
user@xyz.ca"

Default SMTP VS Config (Delivery - Advanced):
FDQN = abc.com

Remote Domain Config:
Allow incoming mail to be relayed to this domain = Yes
Send HELO instead of EHLO = No
Remote domain -> Forward all mail to smart host = [Internal Exchange Server
IP]

[quoted text, click to view]

I doubt that abc.com is the canonical name of this server, so that
could well be a misconfiguration. But that is not in itself causing
the symptoms you describe.

[quoted text, click to view]

You have everything in place here as it should be, so it is possible
that the metabase is corrupt and is not committing these values
properly.

I would recommend that you create a secondary SMTP VS on a different
port and test the same setup on a fresh VS. If it works there, you'll
know the original VS is shaky.