Cyrus IMAP

Cyrus IMAP is an open-source mail server that provides a comprehensive implementation of the Internet Message Access Protocol. It is specifically designed to run on sealed servers where normal users are not permitted to log in to the host operating system, ensuring that the mailbox database is stored in parts of the filesystem that remain private to the Cyrus IMAP system.

The software is deployed as a server application and manages all user access to content through a wide array of standard protocols. It handles the storage and retrieval of email, contacts, and calendar data, allowing multiple concurrent read and write connections to the same mailbox. This architecture is intended to provide high levels of efficiency and administrability for large scale deployments.

Key features

• Support for JMAP, IMAP, NNTP, POP3, CalDAV, CardDAV, and WebDAV protocols
• Private mailbox database design for increased efficiency and scalability
• Implementation of access control lists on mailboxes
• Storage quotas for mailbox hierarchies
• Support for concurrent read and write connections to a single mailbox
• Integration with Xapian for search functionality
• Support for word boundary analysis for Chinese, Japanese, and Korean languages

Cyrus is built for environments requiring high scalability and secure mailbox management. The architecture separates user access from the underlying filesystem, which prevents direct user manipulation of mail files and improves overall system security. It can be installed via source tarballs, git repositories, or through various Linux distribution packages including Debian, Ubuntu, Fedora, Red Hat Enterprise Linux, CentOS, openSUSE, and Gentoo. The project provides specific libraries and dependencies, such as a custom Xapian fork, to enable advanced search features.

This server is intended for system administrators who need a scalable and secure messaging system for managing email, calendars, and contacts across a large user base.