[vox-tech] postgrey is dangerous?

[Bill Broadley]

Sorry to comment late, but I figured I'd throw my input in.

First of all the idea behind grey listing is quite sound, it's an official 
part of the SMTP standard and anyone who can't deal with it is running a 
broken mail server that will fail in many real world scenarios that do not 
involve greylisting.  A please try again later can come up for numerous 
reasons, system load, maintenance windows, system failure, etc.

I've found it to be rather effective, when combined with HELO filtering can be 
quite effective at cutting down the amount of SPAM and makes it much easier to 
run a mailserver that saves the most cpu intensive SPAM/Virus scanning for the 
much reduced traffic that makes it through.  This graph is representative
to what I saw:
     http://postgrey.schweikert.ch/mailgraph_greylisting.png

The compatibility from what I can see is pretty good, I've seen zero problems 
with the bigger systems like yahoo, gmail and the like.  Sure some travel 
agent running some wonky mailserver that he bought as a turnkey package from 
some clueless company 5 years ago might have this incompatibility, but 10%
of his email vanishes into the either because it doesn't handle SMTP properly 
in many ways... but typically such folks adapt and will follow up from a gmail 
account or something.  Real estate agents seem to have similar problems.

Additional documentation for postfix is at:
http://www.postfix.org/SMTPD_POLICY_README.html

The above also includes a sample greylisting daemon if you don't want to use 
postgrey.

Other implementations at:
http://www.greylisting.org/implementations/postfix.shtml