Reverse DNS RFCs and Recommendations

Thu Oct 31 15:13:02 UTC 2013

>Mail admins wanting matching forward/reverse DNS and hostnames that
>don't "look dynamically generated" is probably more of a human than an
>RFC thing:

Right.  Spam filtering depends on heuristics.  Mail from hosts without
matching forward/reverse DNS is overwhelmingly bot spam, so checking
for it is a very effective heuristic.

Mail from hosts with names that look dynamic is also quite spammy, but
figuring out what looks dynamic is quite hard.  I know someone who's been
tuning his regexes for years.  For most people, third party lists like
the Spamhaus PBL are more reliable.

R's,
John