Maildrop is a combination mail filter/mail delivery agent. Maildrop reads the message to be delivered to your mailbox, optionally reads instructions from a file how filter incoming mail, then based on these instructions may deliver mail to an alternate mailbox, or forward it, instead of dropping the message into your mailbox. Maildrop can be installed as your local delivery agent, instead of procmail.
In addition to supporting traditional mailbox files, Maildrop knows how to maildir-based mailbox directories.
Maildrop uses a structured, real, meta-programming language in order to define filtering instructions. Its basic features are fast and efficient. At sites which carry a light load, the more advanced, CPU-demanding, features can be used to build very sophisticated mail filters. Maildrop deployments have been reported at sites that support as many as 30,000 mailboxes. Sample mail filtering recipes as well as complete documentation is provided in both HTML and man page format.