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.
The private mailbox database design gives the server large advantages in efficiency, scalability, and administratability. Multiple concurrent read/write connections to the same mailbox are permitted. The server supports access control lists on mailboxes and storage quotas on mailbox hierarchies.
The Cyrus project is the implementation of IMAP servers by the Carnegie Mellon University Computing Services Department. Over the next few months, we will be releasing components of this server, which will provide better mail security and easier mail administration.
Cyrus IMAP Server distribution
Documentation