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Date:      Thu, 11 Sep 1997 11:49:23 +0930
From:      Greg Lehey <grog@lemis.com>
To:        Dave Babler <dbabler@Rigel.orionsys.com>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Help with Sendmail/DNS
Message-ID:  <19970911114923.00050@lemis.com>
In-Reply-To: <Pine.BSI.3.95.970910180828.3940B-100000@Rigel.orionsys.com>; from Dave Babler on Wed, Sep 10, 1997 at 06:08:59PM -0700
References:  <Pine.BSI.3.95.970910180828.3940B-100000@Rigel.orionsys.com>

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On Wed, Sep 10, 1997 at 06:08:59PM -0700, Dave Babler wrote:
>
> I seem to be banging my head against the wall trying to solve a problem
> and I'm hoping somebody can give me a push in the right direction.
>
> My domain is fairly simple and handles mail straightforwardly. The FBSD
> system is Rigel.orionsys.com and I run a BBS on a machine named
> bbs.orionsys.com (which responds to orionsys.com as well). The BBS can
> send and receive email directly, as can the FBSD machine. The BBS's MX
> records currently look like:
>
> 	orionsys.com.	IN	MX	10 orionsys.com.
> 			IN	MX	20 other.host.com.
> 			IN	MX	30 another.host.com.

You don't have to change the names of the other systems.  This is
public knowledge:

orionsys.com    preference = 10, mail exchanger = orionsys.com
orionsys.com    preference = 20, mail exchanger = portal.dx.net
orionsys.com    preference = 30, mail exchanger = news.dx.net

> The problem is that the BBS software is completely fixed and we're getting
> increasing complaints about spam, so what I'd like to do is to have all
> email going to the BBS users to be delivered to Rigel (the Unix machine),
> passed thru anti-spam filters and then forwarded to the BBS. The BBS would
> still send email directly. To accomplish this, I tried to test the
> concept with another machine in the domain, named Altair:
>
> 	rigel.orionsys.com.	IN	MX	10 rigel...orionsys.com.
> 	altair.orionsys.com	IN	MX	10 rigel.orionsys.com.
>
> This produced a DSN error with sendmail "MX list for altair loops back to
> rigel" for mail sent to user@altair.orionsys.com.

Yes, it would.  Your DNS records are saying "send all mail to altair
by preference to rigel, he'll know what to do with it".  But he
doesn't, and that's the message.

> The examples in the O'Reilly 'DNS and Bind' book don't seem to deal
> directly with the setup I'm trying to do and the Sendmail book
> doesn't specifically over this exact error (although I'm assuming it
> is a looping reference).

I find this book rather unhelpful, in fact.

> Is this idea doomed, or am I just not seeing the right way to
> configure it?

You say that bbs (CNAME for orionsys.com) is the BBS system.  Why do
you want to send mail to altair at all?  I would recommend having MXs
only for orionsys.com (which I wouldn't associate with an A record).
You could then set the MXs to point to rigel, and it could forward to
any of the other systems.

Note that this won't be complete protection against spammers.  They
can always go by the IP address.  But it'll be a while before they're
that sophisticated.

Greg




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