Date: Wed, 20 Dec 2006 12:03:38 +1100 From: Mark Andrews <Mark_Andrews@isc.org> To: freebsd-stable@FreeBSD.ORG Subject: Re: OpenBSD's spamd. Message-ID: <200612200103.kBK13cY6009071@drugs.dv.isc.org> In-Reply-To: Your message of "Tue, 19 Dec 2006 19:35:47 CDT." <20061220003547.GD53372@in-addr.com>
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> On Tue, Dec 19, 2006 at 11:37:26AM -0500, Christopher Hilton wrote: > > Oliver Fromme wrote: > > >Dimitry Andric wrote: > > > > Oliver Fromme wrote: > > > > > What does stuttering mean? Is it similar to sendmail's > > > > > "greet_pause" feature? > > > > > > > > See here: > > > > http://www.ualberta.ca/~beck/nycbug06/spamd/mgp00014.html > > > > > >OK, so the answer to my question seems to be "yes". :-) > > > > > > > Actually I'd say it's similar. If you telnet to port 25 on a server > > that's using sendmail's greet_pause option I'm assuming that you get > > nothing for 5 seconds. OpenSD's Spamd sends the initial greeting at a > > rate of one character per second and only accepts data from you at the > > same rate. > > > > Through experimentation Bob Beck determined that many spammers were > > dropping the connection and forgetting about delivering the mail > > completely after short and shorter intervals if the connection was rate > > limited to 1 character / sec. When the spammers got down to 3 seconds he > > modified spamd to stutter for 10 seconds on any connection. That feature > > came in on OpenBSD 3.8 > > The exim MTA has this comment relating to the SMTP banner > > /* It seems that CC:Mail is braindead, and assumes that the greeting message > is all contained in a single IP packet. The original code wrote out the > greeting using several calls to fprint/fputc, and on busy servers this could > cause it to be split over more than one packet - which caused CC:Mail to fall > over when it got the second part of the greeting after sending its first > command. Sigh. To try to avoid this, build the complete greeting message > first, and output it in one fell swoop. This gives a better chance of it > ending up as a single packet. */ > > I'm wondering how many CC:Mail servers are still out there and if they're > still broken in this regard. That could leave the "stutter" with false > positives.... Broken software is broken software. You can't work around all the bugs in all the broken pieces of software. > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@isc.org
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