22 open-source Business Email & Groupware vendors.

Open-source software for Business Email & Groupware that you can self-host, with auditable source code — regardless of the developer's headquarters.

• Benno MailArchivSelf-hosted / open source

  German, audit-proof enterprise email archiving system for GDPR/GoBD-compliant storage of millions of emails, integrable with any email/groupware system. Developed by LWsystems GmbH (Bad Iburg); core and web app under AGPLv3, some modules proprietary.

  Germany

• CipherMailSelf-hosted / open source

  Amsterdam-developed open-source email encryption gateway that centrally enforces S/MIME, PGP and PDF encryption for all outgoing organisational traffic, acting as a mail proxy between the firewall and internal mail server.

  Netherlands

• Cyrus IMAPSelf-hosted / open source

  Robust, community-maintained enterprise mail and calendar server, suited to organisations with tens of thousands of concurrent users. Originally Carnegie Mellon University (US, 1993); now governed by an independent, mainly US-based governance board, no controlling company.

  United States

• DovecotSelf-hosted / open source

  Open-source IMAP and POP3 server from Finland (Dovecot Oy), part of German Open-Xchange since 2017. High-performance storage and synchronisation of email within enterprise networks.

  Finland · owner in Germany

• EGroupwareEU sovereign

  German open-source groupware platform with email, CRM, project management and more

  Germany

• EximSelf-hosted / open source

  Flexible and highly configurable open-source Mail Transfer Agent, originating at the University of Cambridge (UK) and widely used in complex enterprise environments for advanced email routing. Community-maintained, no controlling company.

  United Kingdom

• grommunioSelf-hosted / open source

  Austrian open-source groupware platform as an alternative to Microsoft Exchange

  Austria

• iRedMailNon-EU vendor

  Open-source mail server installer that sets up a full mail environment (SMTP/IMAP/POP3/webmail) within minutes on RedHat, Ubuntu or Debian. Developed by a Chinese company (iRedMail Information Technology Co., Ltd.).

  China

• KolabEU sovereign

  Swiss open-source groupware platform with email, calendar and file management

  Switzerland

• Mail-in-a-BoxSelf-hosted / open source

  Open-source project (public domain, CC0) that sets up a complete, turnkey mail server appliance, including DNS, SPF, DKIM and Let's Encrypt. Created by Joshua Tauberer (Washington DC, US); no controlling company.

  United States

• MailcowSelf-hosted / open source

  German open-source email server platform with Docker-based installation

  Germany

• MailuSelf-hosted / open source

  Open-source email server in Docker with webmail, anti-spam and antivirus protection

  France

• MoxSelf-hosted / open source

  Modern, Go-based single-binary mail server (MIT licence) that sets up email authentication (SPF, DKIM, DMARC) out of the box. Developed by Mechiel Lukkien (Amsterdam, Netherlands), co-funded by NLnet; no controlling company.

  Netherlands

• Open-XchangeEU sovereign

  German open-source email and groupware platform for providers and companies

  Germany

• PostfixSelf-hosted / open source

  The de facto open-source Mail Transfer Agent (MTA), originally written by Wietse Venema while at IBM's Watson Research Center (US). No controlling company; maintained individually, the foundation of millions of self-hosted mail servers worldwide.

  United States

• Proxmox Mail GatewaySelf-hosted / open source

  Open-source email security solution (AGPLv3 with commercial subscriptions) from Austria's Proxmox Server Solutions GmbH, acting as a mail proxy between the internet and the internal mail server against spam, viruses and phishing. A distinct product from the better-known Proxmox VE virtualisation platform.

  Austria

• RadicaleSelf-hosted / open source

  Lightweight open-source CalDAV and CardDAV server (calendar and contacts, GPLv3), ideal for decoupling from Google/Apple cloud sync. Originated at French web consultancy Kozea; no controlling company in the classic sense, community-maintained.

  France

• RoundcubeSelf-hosted / open source

  open-source webmail-client with modern interface and plugin-architecture

  Switzerland · owner in Germany

• SOGoNon-EU vendor

  Open-source groupware with ActiveSync compatibility and web interface

  Canada

• Stalwart MailNon-EU vendor

  Modern open-source email server written in Rust with JMAP support

  United Kingdom

• Tine 2.0Self-hosted / open source

  German open-source groupware suite (email, calendar, contacts, CRM, HR/personnel management, file sharing) developed and sponsored by Metaways Infosystems GmbH, based in Hamburg. Tine 2.0.Org community edition is licensed under AGPLv3; Metaways offers commercial support, managed hosting (tine20.com/tine20.net), and enterprise editions. Actively maintained as of 2026 with a live commercial offering.

  Germany

• ZimbraNon-EU vendor

  Enterprise email and groupware platform with calendar, contacts and tasks

  United States