On 21/02/2007, at 04:52, Michael Holzt wrote:
If you really want to take this into account, use it as part of a
scoring system (e.g. spamassassin) but not as a sole reason.
I spent a while running myself ragged dealing with legitimate mail from
big ISPs that had no PTR records for their mail servers.
In the end I tweaked spamassassin to give a high score (3.0) to
anything without a PTR. That has worked like a charm because if a
message is even slightly dodgy it will go over the threshold score, but
there's still some headroom to take care of false positives (haven't
had many). I have a similar rule dealing with mail from obvious
dynamic addresses, giving it a score of 3.5
