Re: [Asrg] Wierd reverse DNS resolution might affect spam filters

[Bill Cole <asrg3 at billmail.scconsult.com>]

At 7:26 PM +0100 6/23/06, Tony Finch  imposed structure on a stream 
of electrons, yielding:
> David Wilson <David.Wilson at isode.com> wrote:
> > Some years ago a colleague told me that some resolvers, when doing rDNS
> > lookup with then perform a forward lookup of the hostname, to check that
> > the A records for the name contain the IP address with which you
> > started.
>
> I believe this is usually done in the applications rather than in the
> resolver itself.
>
> > If not true, perhaps it is something which SMTP servers should do
> > themselves, before using the rDNS name for authorization.
>
> What do you mean "perhaps"? Decent MTAs (e.g. Exim) have been doing this
> for many years.

And see http://www.sendmail.org/faq/section3.html#3.38

Note that the date is the date that entry made it into the FAQ, not 
the implementation date. Sendmail has been noting such errors in 
Received headers since 8.8.6, almost exactly 10 years.

Basically, this is a non-issue. Reverse DNS has never really been 
trustworthy, and trusting an unverified rDNS result by itself for 
authentication is an unlikely error for any serious piece of modern 
software.

--
Bill Cole
bill at scconsult.com


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