Sendmail - Increasing the Rejection Criteria

[Scot L. Harris]

On Fri, 2006-03-03 at 08:26 -0600, JHorne wrote:
> I would like my sendmail to reject any emails presented that have a
> mismatched senders email at domain and host.domain.  example:
> 
> Return-Path: <info-c at inkstudio.com>
> Received: from global-change-mail.com (cug31-1-82-234-61-176.fbx.proxad.net
> [82.234.61.176])
> 
> I have been searching for a couple weeks off and on for the answer to this,
> but im having no luck at each attempt.  Can someone shed light on how to
> force sendmail to demand that senders domain match the hosts domain?  With
> rejection if they do not match?  Reverse lookups are already enabled, but
> that seems to only see if the hosts reverse records exists, not whether or
> not the email being sent thru it is authorized.
> 
> If this setting is even possible, yes, I realize the potential for false
> positives, but at this point, in my eyes, this is by far my best solution to
> rejecting spam on my private 5 account email server.
> 
> Thanks in advance,
> jonathan
> 

Take a look at one of the greylisting solutions.  I implemented
milter-greylist at one small business and was able to block about 98% of
the spam that was directed at their server.  Spamassassin catches almost
all of the remainder.

greylisting uses a temp failure code (451), which most spammers do not
handle per the RFC.  That should eliminate most if not all of the type
of messages you are targeting since most spam has forged from
information.