From owner-freebsd-questions@FreeBSD.ORG Thu Oct 16 17:18:23 2008 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id AF7531065690 for ; Thu, 16 Oct 2008 17:18:23 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from smtp.infracaninophile.co.uk (gate6.infracaninophile.co.uk [IPv6:2001:8b0:151:1::1]) by mx1.freebsd.org (Postfix) with ESMTP id DA77C8FC1D for ; Thu, 16 Oct 2008 17:18:22 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from happy-idiot-talk.infracaninophile.co.uk (localhost [IPv6:::1]) (authenticated bits=0) by smtp.infracaninophile.co.uk (8.14.3/8.14.3) with ESMTP id m9GHHVXd027209; Thu, 16 Oct 2008 18:17:32 +0100 (BST) (envelope-from m.seaman@infracaninophile.co.uk) X-DKIM: Sendmail DKIM Filter v2.7.2 smtp.infracaninophile.co.uk m9GHHVXd027209 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=infracaninophile.co.uk; s=200708; t=1224177453; bh=Ho/qE2AhLMr4ly wpP7/IK/oyBqZBxfAJ7sKvQ1/FlQE=; h=Message-ID:Date:From:MIME-Version: To:CC:Subject:References:In-Reply-To:Content-Type:Cc:Content-Type: Date:From:In-Reply-To:Message-ID:Mime-Version:References:To; z=Mes sage-ID:=20<48F77723.9090003@infracaninophile.co.uk>|Date:=20Thu,=2 016=20Oct=202008=2018:17:23=20+0100|From:=20Matthew=20Seaman=20|Organization:=20Infracaninophile|User -Agent:=20Thunderbird=202.0.0.17=20(X11/20080929)|MIME-Version:=201 .0|To:=20eculp@casasponti.net|CC:=20freebsd-questions@freebsd.org|S ubject:=20Re:=20I've=20just=20found=20a=20new=20and=20interesting=2 0spam=20source=20-=20legitimate=0D=0A=20bounce=20messages|Reference s:=20<20081016090102.17qwm4xcs6f4so8ok@intranet.casasponti.net>=09< 20081016145255.GA12638@icarus.home.lan>=09<48F75A88.1000507@infraca ninophile.co.uk>=09=09<20081016173807.64d0f24e@gumby.homeunix.com.>=20<2 0081016115844.17qwm4xcs6jkg84oc@intranet.casasponti.net>|In-Reply-T o:=20<20081016115844.17qwm4xcs6jkg84oc@intranet.casasponti.net>|X-E nigmail-Version:=200.95.6|Content-Type:=20multipart/signed=3B=20mic alg=3Dpgp-sha256=3B=0D=0A=20protocol=3D"application/pgp-signature"= 3B=0D=0A=20boundary=3D"------------enig836C53A80A47A3BC8F209E27"; b=gbLBlOs5AyKPJo9bAX6p9HHiWnfyrpcJClfpVYo9VgZu87Mqr9OQTHY9p3mlBYJNm aE1HHzBExNUKVKjah7CXy7HGm1XP0CX6CBN1IuWjgNQ7MLo+I+qXBT871E832OyP7/E 3Qvi/D4AH8WobVuJ8x4xzlHzuGRFr4KisHaufJA= Message-ID: <48F77723.9090003@infracaninophile.co.uk> Date: Thu, 16 Oct 2008 18:17:23 +0100 From: Matthew Seaman Organization: Infracaninophile User-Agent: Thunderbird 2.0.0.17 (X11/20080929) MIME-Version: 1.0 To: eculp@casasponti.net References: <20081016090102.17qwm4xcs6f4so8ok@intranet.casasponti.net> <20081016145255.GA12638@icarus.home.lan> <48F75A88.1000507@infracaninophile.co.uk> <20081016173807.64d0f24e@gumby.homeunix.com.> <20081016115844.17qwm4xcs6jkg84oc@intranet.casasponti.net> In-Reply-To: <20081016115844.17qwm4xcs6jkg84oc@intranet.casasponti.net> X-Enigmail-Version: 0.95.6 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------enig836C53A80A47A3BC8F209E27" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (smtp.infracaninophile.co.uk [IPv6:::1]); Thu, 16 Oct 2008 18:17:33 +0100 (BST) X-Virus-Scanned: ClamAV 0.94/8434/Thu Oct 16 11:16:49 2008 on happy-idiot-talk.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, score=-2.9 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VERIFIED,NO_RELAYS autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on happy-idiot-talk.infracaninophile.co.uk Cc: freebsd-questions@freebsd.org Subject: Re: I've just found a new and interesting spam source - legitimate bounce messages X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 16 Oct 2008 17:18:23 -0000 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig836C53A80A47A3BC8F209E27 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable eculp@casasponti.net wrote: > RW escribi=F3: >=20 >> On Thu, 16 Oct 2008 08:54:55 -0700 (PDT) >> Luke Dean wrote: >> >>> >>> >>> On Thu, 16 Oct 2008, Matthew Seaman wrote: >>> >>> > Until the wonderful day that the entire internet abides by these >>> > rules[*], use >>> > of technologies like SPF and DKIM can discourage but not entirely >>> > prevent the spammers from joe-jobbing you. >>> >>> I just started getting these bouncebacks en masse this week. >>> My mail provider publishes SPF records. >> >> SPF increases the probability of spam being rejected at the smtp >> level at MX servers, so my expectation would be that it would exacerba= te >> backscatter not improve it. >> >> Many people recommend SPF for backscatter, but I've yet to hear a coge= nt >> argument for why it helps beyond the very optimistic hope that spammer= s >> will check that their spam is spf compliant. >=20 > I feel the same way and thanks for adding some humor to the situation. Most spammers aren't aiming to generate back-scatter as their primary means of disseminating their spam, so they'll do what they can to get the best chance of a successful delivery. That means sending SPF=20 compliant e-mails where possible. It's actually quite simple for them=20 to filter out SPF protected addresses from their target lists, so they=20 do tend to do that, and it's typically the same list of target addresses = they use for forged senders too. It's telling that both having a correct= SPF record and having no SPF record at all have a zero score in SpamAss= assin (ie. neutral) whereas non-compliance scores=20 lots of spam points. Also see my point earlier about rejecting messages during the SMTP=20 dialogue. SPF is easy to check early and lets you reject messages before acknowledging receiving them, which means a lot fewer bounce=20 messages to (probably forged) sender addresses. Cheers, Matthew --=20 Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW --------------enig836C53A80A47A3BC8F209E27 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEAREIAAYFAkj3dysACgkQ8Mjk52CukIy6ZACfad4qwqqZvKL5zaPwHSLZ90jN 9g4AoI3SwLK79H5nZf8lHHvNsTwhzuxi =ifkS -----END PGP SIGNATURE----- --------------enig836C53A80A47A3BC8F209E27--