mail filtering based on reverse DNS

[Bjørn Mork]

"Bjoern A. Zeeb" <bzeeb-lists at lists.zabbadoz.net> writes:
> On Aug 9, 2011, at 4:17 PM, Bjørn Mork wrote:
>
>> Anyway, if you reject mail from IPv6 addresses without reverse DNS
>> today, then you are guaranteed to reject legitimate mail.  One might
>> even question the usefulness of reverse IPv6 DNS as a low score spam
>> rule.  There are just too many matching legitimate sources.
>
> If one operates a legitimate mail server and is unable to provide any reverse
> mapping for the v6 address I seriously do not care to not accept his email as
> it's clearly not operated in a professional manner.

OK.

Sorry for those offended by the real example, but this is one of the
addresses I found in my mail log:

 2001:1890:1112:1::1e

It does have a reverse pointer, so it's half-way there:

 bjorn at canardo:~$ dig +short -x 2001:1890:1112:1::1e
 mail.ietf.org.

but the forward entry does not list that address, so my mail server
ignores the reverse pointer:

 bjorn at canardo:~$ dig +short aaaa mail.ietf.org
 2001:1890:123a::1:1e


So, should I reject mail from 2001:1890:1112:1::1e? Are all those
sending mail from the IETF necessarily unprofessional?



Bjørn