Cyrus IMAP Server

IMAP (Internet Message Access Protocol) is an Internet
standards-track protocol for accessing messages (mail,
bboards, news, etc). The Cyrus IMAP server differs from
other IMAP server implementations in that it is generally
intended to be run on "sealed" servers, where normal users
are not permitted to log in. The mailbox database is stored
in parts of the filesystem that are private to the Cyrus
IMAP system. All user access to mail is through the IMAP,
POP3, or KPOP protocols.