Green Mail Filter is an all-purpose mail processor, it has lots of possible uses. Green is a multi-user server tool that processes users´ mail. Although it comes with a default installation of just one user, it´s by no means limited with that. Green can be thought as a platform for developing mail filters.

In the shortest possible way - Green collects users´ mail messages from somewhere, runs each received message through a set of rules (aka ruleset) and finally puts the message to one of the user´s mailboxes. The primary use for such behaviour was separating legitimate mail (default "mail" mailbox) from spam (default "spam" mailbox).

Green collects user´s mail from external POP3 accounts configured for each user. There is also a separate spooling directory (.spool) for each user, all the files that appear there get collected as well. Spooling messages as plain files can be useful in an environment where mail servers are already in place and filtering needs to be added.

Note: Green is free for personal non-commercial use