Cyrus is an imap server designed to handle massive quantities of mail, with a number of features not found in other imap implementations, including support for:
- running the daemon without root privileges;
- pop3 and nntp in addition to plain imap;
- secure imap using ssl;
- server-side filtering with sieve;
- mail users without login accounts;
- simple mail quotas;
- virtual domains;
- ipv6.
cyrus doesn't support reading from and storing mail in the standard mail spool. it stores mail in a separate directory in its own mh-like format.

this package contains the common files needed by the other cyrus components. the cyrus-imapd and/or cyrus-pop3d packages are needed to enable imap and pop3 support respectively. cyrus-murder can be used to enable imap, pop3 and lmtp proxying. cyrus-replication can be used to provide server replication between two imap servers.