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I've seen my maillog and it has entries like these:

Jul 30 00:51:02 server sendmail[10809]: 0000060000006DF64: to=<>,  delay=05:48:23, xdelay=00:00:00, mailer=esmtp, pri=900000,, dsn=4.0.0, stat=Deferred: Name server: host name lookup failure

Jul 30 00:50:57 server sendmail[5842]: 0000060000007C280: to=<8542@xyz>, delay=03:00:53, xdelay=00:00:05, mailer=esmtp, pri=810000, [x.y.z.d], dsn=2.0.0, stat=Sent (OK id=1V3y9S-0003zn-Fx)

So If I send 100 emails (all auto-generated and not spamming people), ONLY few have been "Sent" and a majority of them are "deferred". The mailboxes exist and the host is reachable with valid MX record.

What is the problem here?

Thank you for time and patience,


share|improve this question
Do you use local (caching) DNS server? – Andrzej A. Filip Jul 30 '13 at 13:27
up vote 1 down vote accepted

It looks like you're having DNS resolution problems. Even the email that was delivered correctly was delayed for over three hours.

Check /etc/resolv.conf on your host to make sure that you don't have non-existent, unresponsive or errant nameservers listed. Make sure that your resolvers respond correctly every time, and set up some periodic monitoring (say every five minutes) to make sure that lookups are succeeding as you'd expect.

If you don't need local or private domain resolution, you could try temporarily changing to Google's nameservers ( and to see if that makes the problem go away.

share|improve this answer
awesome!, that just worked. Thanks a ton. But why is my dns selective in resolving the hostnames? Could it be the load/traffic on it? – Dmartyn Jul 30 '13 at 12:28
Could be any number of things. Maybe that's worth another question (once you've gathered more info) :) – Flup Jul 30 '13 at 12:46

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