IPv6 automatic reverse DNS

Sat Oct 29 01:37:25 UTC 2016

> On Oct 28, 2016, at 6:04 PM, Karl Auer <kauer at biplane.com.au> wrote:
> 
>> 1b) anti spam filters believe in the magic of checking
>> forward/reverse match.
> 
> Someone in this thread said that only malware-infested end-users are
> behind IP addresses with no reverse lookup. Well - no. As long as we
> keep telling anyone who isn't running a full-bore commercial network to
> "consume, be silent, die", we are holding everyone back, including
> ourselves.

If you send mail over IPv6 from an address with no reverse DNS you
will see quite a lot of this sort of thing:

550 5.7.1 [*] Our system has detected that this message
5.7.1 does not meet IPv6 sending guidelines regarding PTR records and
5.7.1 authentication. Please review
5.7.1 https://support.google.com/mail/?p=ipv6_authentication_error for more
5.7.1 information.

> 
> It's fine to use no-reverse-lookup as a component of a spamminess
> score. It's not OK to use it as proof of spamminess.

People running large mailservers made that decision some time
ago. Disagreeing with them won't make them accept your email.

Cheers,
  Steve