	      graymilter - simple graylist mail filter module

Sendmail includes a facility for plugging in custom mail filters,
called milters.  It's documented here: http://www.milter.org/milter_api/
Graymilter uses this facility to implement graylisting.  This is
an idea invented by Evan Harris in 2003.  Basically, the first time
someone tries to send you mail, you send back a temporary failure
response.  A real email system will put the mail into a queue and
re-try it later, at which time the address will have graduated from
the graylist to the whitelist, so the mail will get through.  However,
spam engines and worms do not have real email systems.  They are
optimized for sending out mass quantities of mail, and they generally
do not implement re-trying.  Therefore mail from those sources will
not get through.

The advantages of graylisting are that it's very simple, it requires
zero maintenance, and it will never block any real mail.  The
disadvantage is that it delays mail.  However, people you correspond
with every day will stay in the whitelist and will get through
immediately.  For other folks, well, the delay is brief.

See the manual entry for more details.

Feedback is welcome - send bug reports, enhancements, checks, money
orders, etc. to the addresses below.

    Jef Poskanzer  jef@mail.acme.com  http://www.acme.com/jef/
