The Courier mail transfer agent (MTA) is an integrated mail/groupware
 server based on open commodity protocols, such as ESMTP, IMAP, POP3,
 LDAP, TLS, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and
 mailing list services within a single, consistent, framework.
 .
 The couriermlm command sets up, maintains, and runs a mailing list.
 It automatically handles subscribe and unsubscribe requests, and
 removes undeliverable addresses from the subscription rolls. Mailing
 lists managed by couriermlm require zero human administrative
 oversight. It supports digests, write-only posting aliases, and
 moderated mailing lists.