Date: Mon, 17 Sep 2007 17:48:43 -0700 From: Jay Chandler <lists@sequestered.net> To: freebsd-questions@freebsd.org Subject: Re: SMTP Error from my server? Message-ID: <46EF206B.90908@sequestered.net> In-Reply-To: <4BF548AD-D73A-4822-85D0-B24B03F57E51@mac.com> References: <46EF0243.4000604@chrismaness.com> <46EF0352.9050800@sequestered.net> <46EF0841.8070307@chrismaness.com> <4BF548AD-D73A-4822-85D0-B24B03F57E51@mac.com>
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Chuck Swiger wrote: > > The idea is pretty simple: when someone sends you an email, you delay > accepting it until you can confirm that you can send a reply back to > the sending address, or more precisely, check whether you can do a > MAIL FROM: your domain and RCPT TO: the sender, and have it return OK, > without actually going into the DATA phase and delivering a test message. > > This idea works fine for normal email addresses, but fails miserably > with certain types of automated email which is not intended for people > to reply to, and it also tends to lose out with TDMA > (http://tmda.net/). More importantly, it also fails to work with > itself-- other people using "sender verification callouts" cause a > loop of failed deliveries, as neither side trusts the other. > The larger problem as well is that it doesn't scale. Someone forging a From header out of a botnet could easily DDoS a smaller server completely off the net if enough people implemented this system. Antispam measures that are in and of themselves abusive aren't generally considered to be good ideas. -- Jay Chandler / KB1JWQ Living Legend / Systems Exorcist Today's Excuse: SCSI Chain overterminated
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