The mail filter/mail delivery agent from the Courier Mail suite.

maildrop is a replacement for your local mail delivery agent. maildrop reads a
mail message from standard input, then delivers the message to your mailbox.
maildrop knows how to deliver mail to mbox-style mailboxes, and maildirs.
"maildir" is a mailbox format used by Courier and Qmail.

maildrop optionally reads instructions from a file, which describe how to
filter incoming mail. These instructions can direct maildrop to deliver the
message to an alternate mailbox, or forward it somewhere else. Unlike procmail,
maildrop uses a structured filtering language.

maildrop is written in C++, and is significantly larger than procmail. However,

Authors:
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    Sam Varshavchik <mrsam at courier-mta dot com>