Courier mail server - mail delivery agent

 The Courier mail transfer agent (MTA) is an integrated mail/groupware
 server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP,
 SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list
 services within a single, consistent, framework.
 .
 The maildrop program is a local mail delivery agent.
 it reads a mail message from standard input, then delivers the
 message to the mailbox. It is able to deliver mail to
 mbox-style mailboxes and Maildirs.
 .
 It will optionally read instructions from a file, which describes how
 to filter incoming mail, using a structured filtering language.
 .
 This package is intended for use along with sqwebmail. Otherwise,
 use the standalone maildrop package.