who is using require_rdns.m4?

[Jeff A. Earickson]

On Mon, 6 Jun 2005, Michele Neylon :: Blacknight Solutions wrote:

> Date: Mon, 6 Jun 2005 20:16:32 +0100
> From: "Michele Neylon :: Blacknight Solutions" <michele at BLACKNIGHT.IE>
> Reply-To: MailScanner mailing list <MAILSCANNER at JISCMAIL.AC.UK>
> To: MAILSCANNER at JISCMAIL.AC.UK
> Subject: Re: who is using require_rdns.m4?
> 
> I'd love to do something with this, but I wouldn't like to drop the mail
> entirely, as I know that there would be a silly amount of valid mail dropped
> if I did.

I installed require_rdns.m4 into my sendmail config this morning, and I've
been watching it closely today.  In approx 6 hours, I've rejected (500 error)
nearly 2200 emails, with another 1080 tempfails (400 error) for not resolving
or A/PTR record mismatches.  I've warned our helpdesk about what I did and
why, and I'm waiting for the yelling to begin.  So far, silence.  The bulk
of rejections are from APNIC numbers.  I love watching spammers fail.

>
> How does it handle shared IPs?

I've seen machines with multiple NICs and IPs, but never heard of two machines
sharing the same IP.  Hunh?

> I was reading somewhere that the reverse and forward records have to match,
> which would cause issues in some instances

No reverse DNS = fatal 500 error.  Resolution failures or A/PTR mismatch
are 400 tempfail errors.  In googling on require_rdns.m4, there is some
opinion that A/PTR mismatches should be a 500 error too.  I would agree,
but I'm presently giving mismatches a tempfail error instead.

Jeff Earickson
Colby College

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