Citadel

Spec sheet

Purpose

Citadel is an email, collaboration, groupware, and content-management system.Read 30 Sep 2026 · citadel.org

Deployment

Citadel can run in Docker, through a Linux build script, from source, or via a hosting provider.Read 30 Sep 2026 · citadel.org

Support

Support is provided through an active user and developer community, an online knowledge base, a support forum, and a mailing list.Read 30 Sep 2026 · citadel.org

Architecture

Citadel uses a rooms-based architecture for organizing collaboration features.Read 30 Sep 2026 · citadel.org

Authentication

Citadel can authenticate users through its own database, host-system accounts, or LDAP including Microsoft Active Directory schemas.Read 30 Sep 2026 · citadel.org

Calendar integration

Calendar and address-book functions are available to PIM clients supporting Webcal or GroupDAV.Read 30 Sep 2026 · citadel.org

Core features

The system includes email, calendars, contacts, forums, mailing lists, instant messaging, wikis, blogs, and RSS aggregation.Read 30 Sep 2026 · citadel.org

Docker platforms

The Docker image offers AMD64, i386, ARMv7, and ARM64 builds.Read 30 Sep 2026 · citadel.org

Email clients

Citadel provides built-in SMTP, POP, and IMAP services and works with standards-compliant clients such as Thunderbird and Outlook.Read 30 Sep 2026 · citadel.org

Encryption

Citadel provides TLS encryption for ESMTP, IMAP, POP3, and the Citadel client protocol.Read 30 Sep 2026 · citadel.org

History

Citadel began in December 1981 as a dial-up BBS package written by Jeff Prothero for 8-bit CP/M systems.Read 30 Sep 2026 · citadel.org

Message journaling

Citadel journaling records processed messages but is not itself an archival service, so the project recommends pairing it with a third-party archival product or service.Read 30 Sep 2026 · citadel.org

System requirements

Manual installation requires a modern Unix operating system, root access, Berkeley DB 5 or newer, and libical 3 or newer.Read 30 Sep 2026 · citadel.org

Web access

WebCit provides full access to Citadel through a web browser.Read 30 Sep 2026 · citadel.org

Plans and prices

Every Citadel plan and price →

Where Specifiction places it

• Mail Server Software#4 of 348.3
• Mailing List Management Software#4 of 218.3