Sendmail relay keeps searching DNS

[Madhava]

I have a Linux server running sendmail 8.9.3 behind firewall. The SMTP server (Microsoft IIS) is on the other part of firewall. I need to send all mails to this SMTP server through sendmail. But Sendmail always reports "Host lookup failure"

How to configure sendmail not to look at DNS at all ?

 

[RhythmAce]

First of all you would need to set up the second SMTP (IIS) server as the gateway or mail hub for your host or domain or at least be allowed to use it as such. Then set up a domaintable or mailertable to relay all mail for your domain or host to the other mailserver. Then add this line to /etc/mail/sendmail.mc :

FEATURE(`accept_unresolvable_domains')dnl

Then comment out or delete this line :

dnl FEATURE(`relay_based_on_MX')dnl

Then run m4 to create a new sendmail.cf like this :

m4 /etc/mail/sendmail.mc > /etc/sendmail.cf

This should work for all out going mail. You will still need to setup your domains "MX" record to forward all mail from your domain to the other server or have the other server's "MX" record handle all mail for your domain.

 

[marsd]

Lets see if I have got this right>

You are running sendmail 8.9.x on a ?private?,
subnet separated by a firewall from the "main"
IIS smtp server.

What you do not explain is whether this sendmail
equipped machine is a mail relay for the internal
network or a standalone machine(workstation).

In the former circumstance:
Having sendmail "disregard" dns names or using a
suggestion like the above post is not really your
total solution, if it works at all.
You need to specify a smart_host in your .cf;
and allow relaying to and from this host. This
simply passes all mail traffic on to the primary
mail server and does no processing.
Your firewall rules should not interfere with the transmission of mail traffic to the smtp relay.

In the latter:
Please see the man pages for sendmail and the
null_client option, which was specifically made for circumstances like these. Again you will specify a
smart_host, the external mail.

HTH
M