sendmail host name lookup failure

[Byron Gainey]

I have 2 servers. 1 is the MX host and handles mail. The other has sendmail configured to relay to the MX host for delivery. This has been working for months, but at 5:00 pm on 12/28 it started posting mail.log messages like:

sendmail[3788]: RAA03787: to=someuser, ctladdr=someuser(102/101), delay=00:00:00, xdelay=00:00:00, mailer=relay, relay=mail.mydomain.com,
stat=Deferred: Name server: mail.mydomain.com: host name lookup failure

I have used nslookup from the relaying host and can find the MX host. I can ping the MX host from the relaying host.

It was working, and no changes were made or have been made. What can I look for?

[Sridhar Bhaskarla]

Hi Byron,

You should be able to nslookup in both regular (hostname to IP) and reverse (IP to hostname) on both the servers. Failure in any of the the four combinations will result in the above error. Also, I would check up the mail logs of your smart relay host (mail.mydomain.com) to see if there are any errors. And is it happening to only "someuser" or for all the addresses?. If not, then there might be a problem with the domain propagation of this someuser.

-Sri

[Wodisch]

Hello Byron,

has somebody changed your "/etc/mail/service.switch"?

Just a guess,
Wodisch

[discoverer]

Hello Byron,

I also met a similar issue serveral days ago: nslookup worked but sendmail said host name lookup failure.
After restarting sendmail service it was ok.
(sendmail need to be restarted to read the new config of the name service)

Try it ?

/Discoverer

[Byron Gainey]

The service.switch has been unchanged, and is set for hosts dns files.

I have restarted sendmail numerous times as I try to resolve this problem.

Nslookup on the relay host resolves the MX name to the IP, and the IP to the MX name.

Nslookup on the MX host resolves the relay name to the IP, and the IP to the relay name.

Trace route goes in 1 hop from the relay host to the MX host (2ms time).

I am baffled as to why, and how to workaround.

[Mark Greene_1]

your network guys didn't happen to make a change to your firewall or network mailserver to only look at your ISP's DNS? That happened to me last week, and I had to enable domain masquarading to get around it (the "DM" option in sendmail.cf).

HTH
---
mark

[Sanjay_6 · Accepted solution]

Hi Byron,

Try these links,

http://us-support3.external.hp.com/cki/bin/doc.pl/sid=08067bb910be91def0/screen=ckiDisplayDocument?docId=200000050748268

http://us-support3.external.hp.com/cki/bin/doc.pl/sid=08067bb910be91def0/screen=ckiDisplayDocument?docId=200000014940994

Hope this helps.

Regds

[Byron Gainey]

Sanjay provided the link I was looking for to resolve this issue. Thanks!

I'm not sure why it did not come up when I was querying the knowledge base before posting.

Thanks to all who provided input.

Happy New Year