Cyrus IMAP
Email, contacts and calendar server
Cyrus IMAP is a free and open-source email, contacts, and calendar server that provides access to personal mail, system-wide bulletin boards, news feeds, calendar, and contacts through the IMAP, NNTP, CalDAV, and CardDAV protocols. It is a scalable enterprise groupware system designed for environments from small to large, built on established open standards. Unlike other IMAP server implementations, it runs on sealed nodes where users do not normally log in, with the mailbox database stored in filesystem areas private to the Cyrus IMAP system.
Features include Kerberos, LDAP, and SQL authentication, access control lists, mailbox namespaces, virtual domains, Sieve server-side filtering, delayed delete and expunge, event notifications, CalDAV and CardDAV support, mail spool and mailbox metadata partitions, archiving, quotas, single-instance store, and Cyrus IMAP Murder for server aggregation. It supports JMAP provisionally when built for it, along with antivirus and antispam toolkits, SPF, DKIM, and DMARC deliverability handling, replication, and extensive authentication options through Cyrus SASL.
Cyrus IMAP is intended for small to large enterprise environments, including universities and private enterprise. It is distributed as a package or built from source, with stable and development versions available.
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