	      blackmilter - blacklist 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/
Blackmilter implements a blacklist of IP addresses which are not
permitted to send mail to this host.  Any mail attempts from
blacklisted addresses are rejected immediately upon connection,
before the mail gets transmitted.

This could also be accomplished by turning the blacklists into a
set of firewall rules for port 25.  However, current firewall
implementations process their rules sequentially, one by one.  If
you have a lot of hosts you want blocked, this is too costly.
Blackmilter stores the IP addresses in a data structure that is
both fast and reasonably compact.  If you wanted to, you could
block millions of addresses quite efficiently.

A more reasonable alternative is the access database built into
sendmail.  However, benchmarking shows that blackmilter is much
faster at this task - from thirty to sixty times faster.  If you
are getting a lot of mail and blocking a lot of IP addresses, this
can make a difference.  Also blackmilter has some advantages in
flexibility, such as the autoupdate and socket update features.

Blackmilter does not specify any particular blacklisting policy.
It is merely a clean and simple tool to let you efficiently implement
whatever policy you choose.

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/
