As part of a community effort to avoid reinventing the wheel, the Procmail Module Library provides a collection of useful recipes contributed by Procmail users. The following introduction from the Procmail Module Library http://freshmeat.net/projects/procmail-lib describes the package as:
Procmail Module Library is a collection of many plug-in modules for the Procmail mail processing utility. The modules allow common tasks like parsing dates, times, MIME, and email addresses, forwarding mail, dealing with POP3, spam shielding, running email cron jobs, handling daemon messages, and more.
Each of the modules, or Procmail included files, are comprehensively documented and show example usage. They can be used as supplied, with various configurable options or used as a basis of your own recipes. Many of the techniques we have illustrated in this chapter are used in the library along with some more sophisticated filtering methods based on the type of content within a message...