From owner-freebsd-questions  Tue Apr 14 10:49:33 1998
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Date: Tue, 14 Apr 1998 10:49:30 -0700 (PDT)
From: Dan Busarow <dan@dpcsys.com>
cc: Jeff & Hillary Jones <kf7nn@mutsgo.dyn.ml.org>, questions@FreeBSD.ORG
Subject: Re: domain resolve for email
In-Reply-To: <19980414164844.I1870@freebie.lemis.com>
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On Tue, 14 Apr 1998, Greg Lehey wrote:
> Jeff Jones wrote:
> > I would like to know how to make it so my email accounts
> > do not get mail from unresolveable hosts just like
> > this list.
> 
> I'm no longer sure that this is a good idea.  Over the last couple of
> days I have set up a mailing list, and I find that a large number of
> legitimate users have transient problems in their reverse lookup (not
> their fault, nor of anybody in their domain).  The result is that mail
> to or from them bounces.  I've taken mine out as a result.

The "standard" rule for this returns a temporary error so transient
problems shouldn't do more than slow mail from them down.

Here's the one we use

Scheck_mail
# verify valid DNS entry
R$*             $: <?> $>3 $1
R<?> $* < @ $+ . >      $: <OK>
R<?> $* < @ $+ >        $#error $: 451 Domain must resolve $1@$2 $&{client_addr}

I go through the logs checking these once or twice a month.  Catches
a huge amount of spam and I've only seen one instance where a legit address
was refused. YMMV

You do need to be aware of the potential problems going in but I think 
it is worth it.

Dan
-- 
 Dan Busarow                                                  714 443 4172
 DPC Systems / Beach.Net                                    dan@dpcsys.com
 Dana Point, California  83 09 EF 59 E0 11 89 B4   8D 09 DB FD E1 DD 0C 82


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