Sendmail::Milter provides users with the ability to write mail filters in Perl
that tightly integrate with sendmail's mail filter API.

With this module, you can define and register Perl callbacks with the Milter
engine. This module calls your perl callbacks using interpreters from a
threaded persistent interpreter pool. Milter contexts are presented using an
object-oriented style interface for performing operations on a Milter context.

WWW: http://sourceforge.net/projects/sendmail-milter/