maildrop is a replacement for your local mail delivery agent. It
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 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.

maildrop 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.