mail filtering based on reverse DNS

[Doug Barton]

On 08/10/2011 04:19, Bjørn Mork wrote:
> "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?

Naturally you've reported this to postmaster at ietf.org, right? The
reverses for A and AAAA addresses for mail.ietf.org match, so that
address looks like an anomaly that should be dealt with.


Doug

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