From owner-freebsd-questions@FreeBSD.ORG Wed Mar 14 18:07:27 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 149EB16A403 for ; Wed, 14 Mar 2007 18:07:27 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from mail-out4.apple.com (mail-out4.apple.com [17.254.13.23]) by mx1.freebsd.org (Postfix) with ESMTP id E863613C45B for ; Wed, 14 Mar 2007 18:07:26 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from relay6.apple.com (relay6.apple.com [17.128.113.36]) by mail-out4.apple.com (8.13.8/8.13.8) with ESMTP id l2EI7QIU020737; Wed, 14 Mar 2007 11:07:26 -0700 (PDT) Received: from relay6.apple.com (unknown [127.0.0.1]) by relay6.apple.com (Symantec Mail Security) with ESMTP id A26AB10BB9; Wed, 14 Mar 2007 11:07:26 -0700 (PDT) X-AuditID: 11807124-9b41cbb0000007df-95-45f839dee412 Received: from [17.214.13.96] (cswiger1.apple.com [17.214.13.96]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by relay6.apple.com (Apple SCV relay) with ESMTP id 8644810B61; Wed, 14 Mar 2007 11:07:26 -0700 (PDT) In-Reply-To: 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=US-ASCII; delsp=yes; format=flowed Message-Id: <46E487EC-2AAF-4885-A19E-1D55034C2D4C@mac.com> Content-Transfer-Encoding: 7bit From: Chuck Swiger Date: Wed, 14 Mar 2007 11:07:25 -0700 To: "Chad Leigh -- Shire.Net LLC" X-Mailer: Apple Mail (2.752.2) X-Brightmail-Tracker: AAAAAA== Cc: Christopher Sean Hilton , 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 18:07:27 -0000 On Mar 13, 2007, at 8:37 PM, Chad Leigh -- Shire.Net LLC wrote: >>> Address verification callbacks take various forms, but the way >>> exim does it by default is to attempt to start a DSN delivery to >>> the address and if the RCPT TO is accepted it is affirmative. It >>> is not usually use VRFY. Most address verification is done by >>> attempting to start some sort of delivery to the address. >> >> I'm assuming that DSN is Delivery Service Notification > > yes > >> or return receipt. > > mp Most callback systems either try to do a DSN or they try to do a delivery (SMTP RCPT TO) and then quit before sending a message body via DATA; they do not depend on the SMTP VRFY command as that is commonly blocked or configured to return a generic "I don't know whether the address is valid". >> If it is or if it somehow relies on the ability to deliver a >> message via smtp to *@example.com then I don't see how it prevents >> spam. > > If the mail says it is from chris@vindaloo.com but I cannot send a > DSN to chris@vindaloo.com then the account is most likely bogus > sender and is refused. It works wonders for spam. > > DSN has a specific definition -- look in the RFCs as I don't > remember which RFC it is offhand. But you are supposed to always > accept a DSN from <> as part of the RFCs Supporting bounce messages from <> was part of the original RFC-821/822 specs. The fancier three-digit codes and canonical DSN format was specified somewhat later, but I believe that the updated SMTP RFCs, 2821/2822 include it. -- -Chuck