Sendmail periodically logs: Host unknown

[Lora Ganeva]

Sendmail periodically cannot find hosts with valid e-mail addresses.Checks show that there are MX and A records for this hosts.When I check the system log, no error messaged could be found.

[U.SivaKumar_2]

Hi,

First check whether you can resolve MX records and Address records of the hosts indicated in the error messages.

If you can resolve Address records but not MX records .

enable this option in sendmail.cf

O TryNullMXList

Restart the sendmail.

Now the problem should not come.

If the problem repeats even then , then there is some operational problem with your DNS servers which you have listed in /etc/resolv.conf file of your sendmail server.

regards,
U.SivaKumar

[Birgit Federmann · Accepted solution]

Hi,

this sounds to me like an intermittant DNS server problem. What kind of DNS servers do you have? HP-UX or NT? Do you have forwarders configured? Which sendmail version do you use (what /usr/sbin/sendmail |grep version)?

Kind regards,

Birgit

[Lora Ganeva]

The problem is not with the MX records.This problem occurs periodically and when I try to resolve, everything is ok.
sendmail version is 8.11.1 and bind 9.2.

[Christopher Caldwell]

Give us your DNS topology:
-are the sendmail host and the DNS host the same?
If not look at the remote DNS.

-are either behind a firewall
The DNS could have intermittent connectivity problems through the firewall.

-is the lookup problem specific to certain domains or is it random?
If the lookup problems seem specific to certain domains, the distant DNS probably has a configuration or operational problem.