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,
t 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.