From - Sat Dec  1 08:36:49 2001
To: postfix-users@postfix.org
Subject: Re: Free RBL services??

> # The ignore_mx_lookup_error parameter controls what happens when a
> # name server fails to respond to an MX lookup request. By default,
> # Postfix defers delivery and tries again after some delay. Specify
> # "ignore_mx_lookup_error = yes" to force an A record lookup instead.
> #
> #ignore_mx_lookup_error = no

This refers to the fact that some DNS servers return SERVFAIL instead
of "does not exist" when asked for a MX record.

With ignore_mx_lookup_error = no, Postfix NEVER tries the A record,
with  ignore_mx_lookup_error = yes,  it looks for the A record.