Cyrus IMAP server

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Cyrus IMAP server
Developer(s) Carnegie Mellon University
Stable release
3.0.8[1] / August 10, 2018; 3 days ago (2018-08-10)
Repository Edit this at Wikidata
Written in C
Type Mail Delivery Agent
License original BSD license

The Cyrus IMAP server is electronic mail server software developed by Carnegie Mellon University. It differs from other Internet Message Access Protocol (IMAP) server implementations in that it is generally intended to be run on sealed servers, where normal users cannot log in. The mail spool uses a filesystem layout and format similar to the Maildir format used by other popular email servers such as qmail, Courier, Dovecot, etc. Cyrus IMAP's spool format, said[by whom?] to have improved performance and scalability to Maildir, resides in parts of the filesystem that are private to the Cyrus IMAP system. Users can access mail through the IMAP/IMAP-S, POP3/POP3-S or KPOP protocols.

The Cyrus IMAP server supports server-side mail filtering through the implementation of a mail filtering language called Sieve.

The private mailbox database design gives the server considerable 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.

As of version 2.4.17, there is support for CalDAV and CardDAV to provide an integrated calendaring and email solution, and also support for viewing email via an RSS reader.


Prior to 1994, Carnegie Mellon University exclusively used the locally-developed and non-standard Andrew Messaging System (AMS) for its email communication needs. Originally written in the early 1980s as part of the Andrew Project, it was very advanced for its day. However, it had major scalability issues. Carnegie Mellon wanted to move to a standards-compliant mail system that met or exceeded the feature set of AMS, and with an emphasis on disconnected operation and scalability (scalability both in simultaneous online accesses and in large mailboxes).

In 1994 the Computing Services Division at Carnegie Mellon addressed these goals by starting the Cyrus Project. In 1998, Carnegie Mellon placed all of its incoming freshmen (the class of 2002) on the Cyrus server for the first time. In December 2001, bboard access (which had been mirrored from AMS to Cyrus), cut over to Cyrus completely. AMS was finally phased out in May 2002.

As development on the project progressed, it became clear that users required further scalability and additional reliability beyond that which a single-machine configuration could provide. In response the Computing Services Division developed Cyrus "Murder" clustering,[a] and after several revisions deployed it within Carnegie Mellon in the summer of 2002.

Members of the Cyrus development team at Carnegie Mellon were leaders in the development of large-scale electronic mail infrastructure elsewhere. For example, John Gardiner Myers was Chief Architect of Host Mail Infrastructure at America Online[3] and Rob Siemborski worked on Gmail infrastructure at Google.[4]

In the fall of 2016 Carnegie Mellon announced retirement of Cyrus IMAP as an electronic mail storage service, with Cyrus users required to choose between on-campus Microsoft Exchange mail service and Google "G Suite" off-campus mail hosting.[5] At that time active Cyrus development was ongoing at Fastmail.[6]

See also[edit]


  1. ^ "Releases - cyrusimap/cyrus-imapd". Retrieved 13 August 2018 – via GitHub. 
  2. ^ "Cyrus Murder - Concepts". Appendix C. Retrieved 28 May 2017. 
  3. ^ "John Gardiner Myers". Retrieved 17 February 2018. 
  4. ^ "RFC 4954". Retrieved 17 February 2018. 
  5. ^ "Cyrus Retirement". Retrieved 17 February 2018. 
  6. ^ "Cyrus development and release plans". Retrieved 17 February 2018. 
  1. ^ The term "murder" is borrowed from the commonly-used collective noun for crows.[2]

External links[edit]