Milter-greylist

Hi,

I seem to remember that I've heard Emmanuel talk about implementing 
greytrapping, but I've not seen it discussed here. I've tried to 
implement that in mimedefang, but there are some drawbacks that could be 
  avoided by using milter-greylist for that.

There are at least two ways to trap spammer IP's:

o messages sent to e-mail addresses that never existed (and will never 
exist) in the destination domain.
  An amazingly common case is spam received to e-mail addresses that are 
in fact message-id of usenet posts where XEmacs/GNUS was used, you get 
messages addressed to things like  "wzizo1at5ti.fsf@...". The IP of 
this sender can sent to an acl to be  blocked for an extended delay...

o messages sent to the lowest priority MX of a site when a higher 
priority MX is alive. One trick to detect that is to assign 2 IP 
addresses to you main MX and to declare the second one as another MX for 
your domain(s) with a very low priority. Now when a t-uple arrives to 
this IP and has not been seen by milter-greylist before (using the 
lazywaw or the subnetmatch feature if needed), it's for sure something 
that violates the RFC and deserves to wait longer (or get rejected 
directly).

I think those 2 kinds of trap are pretty easy to implement, and I'm 
willing to try to give them a shot, unless someone else beats me or 
finds this really stupid and useless.

-- 
Matthieu Herrb