error: Host unknown, please help!

[Tilman Schmidt]

At 08:58 30.03.00 -0800, Jeremy wrote:
>Whenever I send a message to mail to user123 at mydomain.com I get a return
>response from *somewhere* with the "Transcript" of:
>
>550 mailto:user123 at mydomain.com...  Host unknown (Name server:
>my.ip.add.ress.mydomain.com.: no data known)

Your obfuscation of the real information makes a diagnosis rather
difficult, so I may be completely wrong, but the little that's left
looks like your zone file for mydomain.com contains a line like:

@       MX 10 my.ip.add.ress

That is, you wrote the IP address instead of the host name of your
mail server into your MX record.

-- 
Tilman Schmidt          E-Mail: Tilman.Schmidt at sema.de (office)
Sema Group Koeln, Germany       tilman at schmidt.bn.uunet.de (private)