Cyrus IMAP

OPEN SRC

The complete, scalable, and open-source email, contacts, and calendar server.

► Large organizations needing robust, scalable email and calendaring

VG SCORE

7.0

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Product Details

PricingOpen Source

API✅ REST

Learning CurveSteep

Integrations13 available

■ INTELLIGENCE BRIEFING — Weekly tool drops. No spam.

PROS & CONS

STRENGTHS

Enterprise-grade scalability and reliability proven in large installations.
Actively maintained with strong community and commercial support.
Extremely scalable and proven in large, demanding environments.

WEAKNESSES

−Lacks a built-in webmail client, requiring integration with separate projects like Roundcube.
−Steep learning curve; configuration is complex for non-experts.

KEY FEATURES

Unified Storage (Sieve)

Uses a single-store 'Sieve' backend for mail, calendar, and contact data.

Scalable Architecture

Designed for large-scale deployments with high concurrency and data volume.

High Scalability

Designed to handle massive mailboxes and high user loads efficiently.

CalDAV & CardDAV Support

Full support for calendar and contact synchronization via open standards.

WHO IS Cyrus IMAP BEST FOR?

System administrators at universities or large enterprises

They need a scalable, secure, and standards-compliant mail server to manage email, contacts, and calendars for thousands of users.

Developers and IT teams building custom email solutions

They require a robust, open-source platform with extensive protocol support (IMAP, CalDAV, CardDAV) to integrate email and scheduling into applications.