[wplug-internet] Postfix greylisting

[Vance Kochenderfer]

Ted covered the basics.  An additional detail is that postgrey
tracks the triplet [client IP address, SMTP sender, SMTP
recipient] for incoming messages.  If it is the first time a
triplet has been seen, it will return a temporary 450 error.  When
the sender tries again with the same triplet, the message is
accepted (there is a brief time interval required to foil spambots
that just repeatedly try to slam through the same message).

Once a particular triplet is accepted, further messages with that
triplet are automatically accepted with no delay.  If a particular
triplet has not been seen for a month or so, it is forgotten and
the process starts over.

Some minor gotchas are that because each of the WPLUG lists has a
different e-mail address, mail to them has different triplets.  So
if one of your posts is accepted to one list, that doesn't help
you when trying to post to another.  The other problem can occur
if the IP of your mailserver changes frequently.  Each time the IP
changes, that invalidates all the triplets it used to have.  If
you find that your server (or another legitimate one) has trouble
getting through, we can add it to the whitelist.

The reason we use it is because it is incredibly effective at
stopping spam, and doesn't require the massive memory/CPU
resources and maintenance that content scanning does.

Vance Kochenderfer        |  "Get me out of these ropes and into a
vkochend at nyx.net          |   good belt of Scotch"    -Nick Danger