A private BSD laboratory

I had setup a front-end SMTP relay system one more time, running on the latest release currently in the stable branch of the FreeBSD Project development (6.2).
I’m a bit experienced in running Sendmail on BSD systems, so I spent only few minutes to configure and test e-mail routing, and I took some time for having a look at a strange behavior that I’m not be able to understand yet.

Think as if the host name was mx2.mydomain.com: since I had to build it as a secondary mail exchanger for several email domains, after the insertion of all the domains in the relay-domains Sendmail configuration file, I wrote in the mailertable to have all messages sent to these domains relayed to the primary SMTP inbound server (maybe located in a different location), by inserting this lines:

With this config, delivery problems came for the messages sent to the first domain, whereas all mail sent to others domains were successfully relayed. The error messages that appeared in the log files were suggesting a clear matter: “stat=Deferred: Name server: mx1.mydomain.com : host name lookup failure”. This should not leave you any doubt, but after I checked there was not any name resolution problem, I found that a bit strange: in fact, why only delivering to the first domain was faulting?
I decided to change the mx1.mydomain.com name with its corresponding IP address, and all worked fine, for all domains!

After a lot of testing, I found that Sendmail seems not to be able to relay any message to the primary MX if its FQDN lies in the same DNS domain of the Sendmail host!! I posted this unbelievable matter in the comp.mail.sendmail newsgroup, but I haven’t got any reply yet… please someone show me that the problem is due only to an error in my configuration: I cannot believe there is such a serious bug in Sendmail without anyone has ever noticed it! :S