Subdomain novice issue

From: Jim Aptal (aptal@trnet.tr)
Date: 04/03/03 

From: "Jim Aptal" <aptal@trnet.tr>
Date: Thu, 3 Apr 2003 11:20:36 +0300

Hello. At first please forgive me for the simplicity of my question,
but I'm rather new to this kind of stuff. I use Red Hat Linux 8.0.
I am trying to set up a subdomain, sub.domain.com, to install a separate
mail server,
named say subsrv.
But the machine which will store this belongs to domain.com, not
sub.domain.com.
(I have also tried the machine to be member of sub.domain.com with the same
results).

My main MX records are as follows:

domain.com. IN MX 100 srv.domain.com
                            IN MX 200 topleveldns.domain.com

I have included the following in my main mydomain.com zone:

sub.domain.com. IN NS srv.domain.com
                              IN MX 150 subsrv.domain.com

I have also included the following in the new server's
/etc/mail/local-host-names:

subsrv.domain.com

The problem is that sendmail complains about the usual issue "MX list for
sub.domain.com points
back to subsrv.domain.com". I tried to change the contents of
/etc/mail/local-host-names to

sub.mydomain.com

but this results in sendmail to hang when trying to send mail to any
user@sub.domain.com.

Is there something I am doing wrong? I would appreciate any help.

Thank you
Jack