From spamassassin-talk-admin@lists.sourceforge.net Fri Sep 13 20:45:28 2002 Return-Path: Delivered-To: yyyy@localhost.spamassassin.taint.org Received: from localhost (jalapeno [127.0.0.1]) by jmason.org (Postfix) with ESMTP id 7E44416F03 for ; Fri, 13 Sep 2002 20:45:27 +0100 (IST) Received: from jalapeno [127.0.0.1] by localhost with IMAP (fetchmail-5.9.0) for jm@localhost (single-drop); Fri, 13 Sep 2002 20:45:27 +0100 (IST) Received: from usw-sf-list2.sourceforge.net (usw-sf-fw2.sourceforge.net [216.136.171.252]) by dogma.slashnull.org (8.11.6/8.11.6) with ESMTP id g8DJ6lC31348 for ; Fri, 13 Sep 2002 20:06:47 +0100 Received: from usw-sf-list1-b.sourceforge.net ([10.3.1.13] helo=usw-sf-list1.sourceforge.net) by usw-sf-list2.sourceforge.net with esmtp (Exim 3.31-VA-mm2 #1 (Debian)) id 17pvjp-0007DC-00; Fri, 13 Sep 2002 12:04:21 -0700 Received: from eclectic.kluge.net ([66.92.69.221]) by usw-sf-list1.sourceforge.net with esmtp (Cipher TLSv1:DES-CBC3-SHA:168) (Exim 3.31-VA-mm2 #1 (Debian)) id 17pvi8-0001P9-00 for ; Fri, 13 Sep 2002 12:02:36 -0700 Received: from eclectic.kluge.net (localhost [127.0.0.1]) by eclectic.kluge.net (8.12.6/8.12.6) with ESMTP id g8DJ1I4q022972; Fri, 13 Sep 2002 15:01:18 -0400 Received: (from felicity@localhost) by eclectic.kluge.net (8.12.6/8.12.6/Submit) id g8DJ1I96022970; Fri, 13 Sep 2002 15:01:18 -0400 From: Theo Van Dinter To: vernon@comp-wiz.com Cc: spamassassin-talk Subject: Re: [SAtalk] OT: DNS MX Record Clarification Please Message-Id: <20020913190117.GG5897@kluge.net> References: <20020913151635.M21128@b2unow.com> <20020913183343.M49078@b2unow.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Fnm8lRGFTVS/3GuM" Content-Disposition: inline In-Reply-To: <20020913183343.M49078@b2unow.com> User-Agent: Mutt/1.4i X-GPG-Keyserver: http://wwwkeys.pgp.net X-GPG-Keynumber: 0xE580B363 X-GPG-Fingerprint: 75B1 F6D0 8368 38E7 A4C5 F6C2 02E3 9051 E580 B363 Sender: spamassassin-talk-admin@example.sourceforge.net Errors-To: spamassassin-talk-admin@example.sourceforge.net X-Beenthere: spamassassin-talk@example.sourceforge.net X-Mailman-Version: 2.0.9-sf.net Precedence: bulk List-Help: List-Post: List-Subscribe: , List-Id: Talk about SpamAssassin List-Unsubscribe: , List-Archive: X-Original-Date: Fri, 13 Sep 2002 15:01:18 -0400 Date: Fri, 13 Sep 2002 15:01:18 -0400 --Fnm8lRGFTVS/3GuM Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Sep 13, 2002 at 01:33:43PM -0500, vernon wrote: > As I understand it, DNS A records are used in a rotating fashion for load > balancing, but DNS MX records are used in order or prority, meaning the 10 > before the 20 and only 20 if the 10 isn't available. That's the theory, yes. > But only some of the mail is actually being scanned which leads me to > believe that not all of the mail is actually hitting that box and the 10 > never goes down. Why? Have I got something confused here? No, but either due to some technical glitch, or downright just wanting to do so, people send to the secondary. It's a semi-usual spammer trick actually to bypass the main server and send directly to a secondary since it will either have less filtering, or be "trusted", or ... MX records in the mail world are all explained in RFC 2821, section 5: [...] Multiple MX records contain a preference indication that MUST be used in sorting (see below). Lower numbers are more preferred than higher ones. If there are multiple destinations with the same preference and there is no clear reason to favor one (e.g., by recognition of an easily-reached address), then the sender-SMTP MUST randomize them to spread the load across multiple mail exchangers for a specific organization. [...] If it determines that it should relay the message without rewriting the address, it MUST sort the MX records to determine candidates for delivery. The records are first ordered by preference, with the lowest-numbered records being most preferred. The relay host MUST then inspect the list for any of the names or addresses by which it might be known in mail transactions. If a matching record is found, all records at that preference level and higher-numbered ones MUST be discarded from consideration. If there are no records left at that point, it is an error condition, and the message MUST be returned as undeliverable. If records do remain, they SHOULD be tried, best preference first, as described above. --=20 Randomly Generated Tagline: "Now let's say I like sheep... And now let's say I take the sheep to a=20 Christmas party..." - Bob Golub --Fnm8lRGFTVS/3GuM Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE9gjX9AuOQUeWAs2MRAg7PAJ42kO68knZx76oQbrZPMGdg/JbJHACfQvlX O/Utl8FY01aS+/e3VNE9WWM= =O6kU -----END PGP SIGNATURE----- --Fnm8lRGFTVS/3GuM-- ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Spamassassin-talk mailing list Spamassassin-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spamassassin-talk