Strange sendmail behaviour

[Marcelo Medici <gaucho@ericps.crc.uiuc.edu>]

I have an interesting sendmail scenario. I am testing out MX records in a
lab. I have three hosts:

 a.test.lab
 b.test.lab
 c.test.lab

b and c both act as secondary mx for a. each has a dns entry. they each
also have cname entries as mx1.test.lab and mx2.test.lab respectively.

dns is configured for db.test.lab as

@	IN	MX 10 a.test.lab
     	IN	MX 20 mx1.test.lab
	IN	MX 30 mx2.test.lab

i test their ability to act as secondary mail server by sending a message
with the following as the recipient:

 gaucho%test.lab@b.test.lab

this works properly and the mail arrives to a.test.lab in the gaucho
inbox.

oddly, when i send a message to

 gaucho%test.lab@mx1.test.lab

the message is bounced saying that there is a local configuration problem
on the mx1 machine. neither b.test.lab nor mx1.test.lab have reverse
lookup entries in dns. i had at first thought that there was a problem
with forward and reverse entries not matching. this does not seem to be
the case.

Each secondary machine is configured with a /etc/mail/relay-domains with a
single line:

test.lab

I have also tried using the /etc/mail/access file as a relay authority
with

test.lab RELAY

in the file. Still, same outcome.

Each machine has an empty /etc/mail/local-host-names

Can someone provide insight as to what is occurring and how to fix this
such that mail sent to @mx1.test.lab will properly be relayed? All
machines are running RedHat 7.3 and the lastest patched sendmail RPM
available from RedHat.

Thank you.


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