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In-Reply-To: <op.vihk8tzvtfhldh@rbeam.xactional.com> From: Claudio Lapidus <clapidus@gmail.com> Date: Sun, 5 Sep 2010 14:36:30 -0300 To: Ricky Beam <jfbeam@gmail.com> Cc: NANOG list <nanog@nanog.org> Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org Hello all, On Fri, Sep 3, 2010 at 11:30 PM, Ricky Beam <jfbeam@gmail.com> wrote: > > If I block port 25 on my network, no spam will originate from it. > (probablly) The spammers will move on to a network that doesn't block the= ir > crap. =A0As long as there are such open networks, spam will be rampant. = =A0If, > overnight, every network filtered port 25, spam would all but disappear. > =A0But spam would not completely disappear -- it would just be coming fro= m > known mailservers :-) =A0thus enters outbound scanning and the frustrated= user > complaints from poorly tuned systems... > That won't be probably the case. Here recently we conducted a rather comprehensive analysis on dns activity from subscribers, and we've found that in IP ranges that already have outgoing 25 blocked we were still getting complaints about originating spam. It turned out that the bots also know how to send through webmail, so port 25 blocking renders ineffective there. --cl.
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