maildrop is the mail filter/mail delivery agent that's used by the
Courier Mail Server. This is a standalone build of the maildrop mail
filter that can be used with other mail servers.
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.
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, it uses resources much more efficiently. Unlike
procmail, maildrop will not read a 10 megabyte mail message into
memory. Large messages are saved in a temporary file, and are filtered
from the temporary file. If the standard input to maildrop is a file,
and not a pipe, a temporary file will not be necessary.
maildrop checks the mail delivery instruction syntax from the filter
file, before attempting to deliver a message. Unlike procmail, if the
filter file contains syntax errors, maildrop terminates without
delivering the message. The user can fix the typo without causing any
mail to be lost.