Greylisting

[Bill McGonigle]

Is anybody using Greylisting on their mailservers?  It sounds like a 
great idea.

Roughly:

	* incoming mail gets scanned for envelope sender, envelope recipient, 
sending IP
	* if it's the first time the tuple is seen it gives an SMTP 'temporary 
failure' error.  The sending MTA retrys.
	* if it's been seen before it's accepted

Reportedly, most mass-Spamming tools will just drop the attempt if it's 
not immediately successful. People are reporting 95% reductions of 
input to SpamAssassin, et. al.  I'm not sure if it makes economic sense 
for spammers to deal with temporary errors.  So this countermeasure has 
some arms-race problems, but perhaps fewer than most anti-spam 
techniques.  Obviously a critical mass will push it over the edge at 
some point.
	
   http://projects.puremagic.com/greylisting/whitepaper.html
   http://isg.ee.ethz.ch/tools/postgrey/

Listed broken MTA's:

     Novell Groupwise 6.0 - Confirmed
     InterMail 4.0 - Reported
     ISMail - Reported

I'm willing to give it a go, just looking for any "don't even think 
about it because..." stories.

-Bill
-----
Bill McGonigle, Owner           Work: 603.448.4440
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