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Subject Spam filtering similar to SPF, less breakage
Date Tue, 09 Feb 2010 03:08:10 GMT
You get an email delivered from (last untrusted
relay).  You look up the DNS A record for that IP, and get  Then you look up the DNS PTR record of, and if it's, it's a legit email sender and gets some negative SA score.
Otherwise it's not, and gets some positive SA score (low at first until
adoption spreads).

So it's not tied to the SMTP MAIL FROM or anything.
Forwarding doesn't break.

Eventually you reject all email from IPs without such records.

Obviously you'd need a blacklist of spammer domains that list spamming
IPs as legit senders.  Not an RHSBL / MAIL FROM blacklist, but a blacklist
where, when the A record of a delivering IP is in a blacklisted domain, the
mail gets rejected.

I am not at all attached to the format of the PTR record and would
like suggestions.

Is there any way this wouldn't be very useful?

"Of course there's strength in numbers. But there's strength in sharp
weaponry too. Ironically, this lead to what we call 'civilization'."
- spore

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