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Huge spam decline due to greylisting?

From: Bob Proulx
Subject: Huge spam decline due to greylisting?
Date: Sat, 27 Jan 2007 10:35:32 -0700
User-agent: Mutt/1.5.9i

Starting sharply on Wednesday there has been a marked decline in the
amount of spam flowing through listhelper.  I had a message from
Ward Vandewege on Tuesday saying:

  We've just enabled a new antispam measure. Basically we've actived
  passive OS fingerprinting (using p0f) combined with selective
  5-minute greylisting (only for hosts detected to be running
  [...selected operating systems...]).

This must have made a huge difference because looking at the stats
show a significant decline in spam at that time.  Wow!  That was a
really significant change.  My server went from being almost fully
utilized continuously to having some free cpu cycles again.

However the reason Ward was sending me that information is because as
he says my machine is being reported as being all types of operating
systems and was asking if I was trying to hide the os type?  But I am
not doing anything actively at all to disguise my machines operating
system type.  It is basically a stock Debian GNU/Linux machine.

Therefore I suspect that the fingerprinting is not working as intended
and greylisting only the selected systems.  I suspect that instead the
effect is that all systems are now greylisted!  I think we are just
seeing the normal (positive) effect of spam reduction that everyone
reports when enabling greylisting.  I am inclined to cheer about this
at this point.  (Even if it is the result of a bug in the system
catagorizing every system as suspect rather than an active design
choice simply to greylist all.)



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