From owner-freebsd-questions@FreeBSD.ORG Wed Mar 14 03:37:02 2007 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 2076916A400 for ; Wed, 14 Mar 2007 03:37:02 +0000 (UTC) (envelope-from chad@shire.net) Received: from hobbiton.shire.net (mail.shire.net [166.70.252.250]) by mx1.freebsd.org (Postfix) with ESMTP id 096A213C44B for ; Wed, 14 Mar 2007 03:37:01 +0000 (UTC) (envelope-from chad@shire.net) Received: from [67.171.127.191] (helo=[192.168.99.68]) by hobbiton.shire.net with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.51) id 1HRKIP-000GsJ-DE; Tue, 13 Mar 2007 21:37:01 -0600 In-Reply-To: <45F76C4B.5070905@vindaloo.com> References: <20070311200829.31802.qmail@simone.iecc.com> <0AC225E6-E55D-4C20-9A00-2EDD95985848@shire.net> <20070311165028.S44863@simone.iecc.com> <45F57936.3030601@usm.cl> <1173830431.1588.34.camel@dagobah.vindaloo.com> <30DC016D-CA46-44D1-A12D-00BDD723A71D@shire.net> <45F76C4B.5070905@vindaloo.com> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed Message-Id: Content-Transfer-Encoding: quoted-printable From: "Chad Leigh -- Shire.Net LLC" Date: Tue, 13 Mar 2007 21:37:00 -0600 To: Christopher Sean Hilton X-Mailer: Apple Mail (2.752.2) X-SA-Exim-Connect-IP: 67.171.127.191 X-SA-Exim-Mail-From: chad@shire.net X-SA-Exim-Scanned: No (on hobbiton.shire.net); SAEximRunCond expanded to false Cc: Marcelo Maraboli , User Questions Subject: Re: Tool for validating sender address as spam-fighting technique? 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: Wed, 14 Mar 2007 03:37:02 -0000 On Mar 13, 2007, at 9:30 PM, Christopher Sean Hilton wrote: > Chad Leigh -- Shire.Net LLC wrote: >> On Mar 13, 2007, at 6:00 PM, Christopher Sean Hilton wrote: >>> On Mon, 2007-03-12 at 12:00 -0400, Marcelo Maraboli wrote: >>> >>>> >>>> I agree..... callbacks are not enough, you can reach a >>>> false conclusion, that=B4s why I use SPF along with callbacks... >>>> >>>> on the same message, my MX concludes: >>>> >>>> "you are sending email "from chad@shire.net", but shire.net >>>> says YOUR IP address is not allowed to send email on behalf >>>> of that domain, therefore YOU ARE FAKE/FORGED" ..---> reject >>>> >>>> regards, >>>> >>> >>> I'm not sure what you mean by callbacks but if that involves =20 >>> talking to >>> mx.example.com and trying to figure out if =20 >>> cmdr.sinclair@example.com is >>> a valid address go ahead. I would consider a mailserver that answers >>> that question a security risk as it is freely giving away =20 >>> information >>> about your domain without notifying you. For a long time my mx =20 >>> servers >>> would answer any such question in the affirmative regardless of =20 >>> whether >>> or not the mail account existed. >> Address verification callbacks take various forms, but the way =20 >> exim does it by default is to attempt to start a DSN delivery to =20 >> the address and if the RCPT TO is accepted it is affirmative. It =20 >> is not usually use VRFY. Most address verification is done by =20 >> attempting to start some sort of delivery to the address. > > I'm assuming that DSN is Delivery Service Notification yes > or return receipt. mp > If it is or if it somehow relies on the ability to deliver a =20 > message via smtp to *@example.com then I don't see how it prevents =20 > spam. If the mail says it is from chris@vindaloo.com but I cannot send a =20 DSN to chris@vindaloo.com then the account is most likely bogus =20 sender and is refused. It works wonders for spam. DSN has a specific definition -- look in the RFCs as I don't remember =20= which RFC it is offhand. But you are supposed to always accept a DSN =20= from <> as part of the RFCs Chad --- Chad Leigh -- Shire.Net LLC Your Web App and Email hosting provider chad at shire.net