[Mimedefang] Powerful anti-spam rule that never discards valid e-mail

[Albert E. Whale, CISSP]

How do I develop the List of From Databases for MIMEDefang?

David F. Skoll wrote:

>Hi,
>
>As part of the development of my commercial anti-spam solution CanIt
>(http://www.canit.ca/), I discovered a powerful anti-spam rule that I'm
>sharing with the MIMEDefang community.
>
>Empirical evidence suggests about 35-45% of spammers use special software
>to spam from home computers rather than relaying through legitimate MTA's.
>More empirical evidence tells me that this special spamware ignores
>temporary-failure codes, never retrying a failed message.
>
>Therefore, CanIt allows you to return a temporary-failure code at the
>MAIL FROM: phase for a sender you've never seen before.  (It keeps a
>database of all known MAIL FROM: senders, and tempfails new entries.)
>If you have many people at your site, you can keep a database of MAIL
>FROM: per RCPT TO:, and do the tempfail at the RCPT TO: phase.  (Your
>database may grow rather large in this case.)
>
>If you're worried about legitimate mail being delayed, just give your
>mail server another IP address and publish it as a secondary MX record.
>Legitimate MTA's will immediately fall back to the "secondary" MX,
>and will be accepted (the MAIL FROM: is already known, now.)  Spamware
>will never retry.
>
>Try it.  This simple rule is amazingly effective.  I should probably
>patent it, but I hate software patents, and I'm disclosing it now
>to establish prior art in case someone else tries patenting it. :-)
>
>--
>David
>_______________________________________________
>MIMEDefang mailing list
>MIMEDefang at lists.roaringpenguin.com
>http://lists.roaringpenguin.com/mailman/listinfo/mimedefang
>
>  
>

-- 
Albert E. Whale - CISSP
http://www.abs-comptech.com
----------------------------------------------------------------------
ABS Computer Technology, Inc. - ESM, Computer & Networking Specialists
Sr. Security, Network, and Systems Consultant
Board of Directors - InfraGard - Pittsburgh, PA