Maildrop is the mail filter/mail deilvery agent that's used by the Courier Mail Server.
It 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 the Qmail MTA.
Maildrop will optionally read instructions from a file, which describes how to filter incoming mail. Instructions can be provided having mail delivered to alternate mailboxes, or forwarded somewhere else. Unlike procmail, maildrop uses a structured filtering language.
It is written in C++, and is significantly larger than procmail in compiled form. 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. Temporary files are saved in the user's home directory. If the standard input to maildrop is a file, and not a pipe, a temporary file will not be necessary.
It checks the syntax of the mail delivery instructions 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.
