> I have an Exim instance running on Debian Jessie. For each mail that is
> received by Exim I would like to check if the reverse DNS for the sender
> domain matches the connecting IP and if not reject the mail.
>
> Consider the following scenarios.
> * A spammer sends an email from the IP 94.123.123.123 with
> info@??? in the "From" field but the domain
> spammerwebsite.com doesn't resolve to 94.123.123.123. I want this to be
> blocked.
This will bounce a great deal of perfectly legitimate email from a lot
of domains, even with quite loose matching.
> P.S.
> * Where can I find the correct documentation?
http://www.exim.org/, see the Documentation link. Yes, you will have to
read much of the large manual.
> * Why can't the configuration start from an empty file?
Various people will have various answers, but my answer is that it
doesn't because Exim is a mailer construction kit. It is not doing
anything when you start it with an empty configuration file for the
same reason that a construction firm is not going to do anything if
you say 'build me something' without specifying what you want built.
- cks
