Cyrus IMAP is a robust open-source email, contacts, and calendar server designed for businesses of all sizes, including nonprofits and government organizations. It offers a subscription-based licensing model, making it accessible for various user types. Key features include high-speed performance, enhanced security measures, and efficient data handling capabilities. The server supports CardDAV and CalDAV protocols, allowing seamless synchronization of contacts and calendars, and is built to handle large installations with scalable architecture.

In addition to its core functionalities, Cyrus IMAP provides flexible filtering options through Sieve and supports antivirus and antispam toolkits, ensuring secure email communication. The software also facilitates deliverability with support for SPF, DKIM, and DMARC standards. Extensive authentication options via Cyrus SASL and JMAP support further enhance its capabilities, making Cyrus IMAP a versatile solution for managing email and calendar services.