Mailfromd is a general-purpose mail filtering daemon for Sendmail, Postfix,
and MeTA1.  It is able to filter both incoming and outgoing messages using
criteria of arbitrary complexity, supplied by the administrator in the form
of a script file.  The daemon interacts with the MTA via Milter or PMilter
protocols.  Some of its features:

  - Flexible programming language for writing MTA extensions
  - Sender address verification (call-out)
  - Greylisting and whitelisting
  - Mail sending rate control
  - Local account verification
  - Native language support

WWW: http://puszcza.gnu.org.ua/software/mailfromd/