reverse dns configuration for IPV4, IPV6+ dns+ mail ?

John Levine johnl at
Mon Jun 19 12:39:50 UTC 2017

In article <mailman.302.1497854956.702.bind-users at> you write:
>>* IP with *one* PTR
>>* the A-Record for the PTR matches
>>* smtp_helo_name of your MTA matches the same name
>Even this is not required. In fact, requiring this breaks SMTP RFC.
>The only requirement on helo name is that host must exist and be canonical,
>which means it has to point to A or AAAA record.

Regardless of what the RFC says, if an IP doesn't have matching
forward/backward DNS that is an extremely strong indication that it's
a random computer in a botnet and few people will accept mail from it.

As others have noted, it doesn't matter what the forward/backward name
is so long as at least one pair of A and PTR match.  You do want the
HELO name to resolve correctly, again, again non-resolving HELO is a
very strong indication of a bot.

Yes, we know the SMTP specs say otherwise but they haven't been
updated since bot spam became such a problem.


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