Thanks to Mail::Audit for:

- Showing that reasonable mail filters can be written in a scripting
  language.

Thanks to TMDA for:

- Showing that an aggressive SPAM heuristic coupled with a
  confirmation system is an effective technique for reducing SPAM.
- The idea of tacking on an HMAC to address extensions
  (Mail::AddressTagger).

Joakim Andersson - Initial implementation of the filter method.
Pavel Kolar - but report (1.8.0 incompatability)