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Draft:Grommunio

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  • Comment: In accordance with the Wikimedia Foundation's Terms of Use, I disclose that I have been paid by my employer for my contributions to this article. Mekromer (talk) 20:51, 16 June 2026 (UTC)
grommunio
Developergrommunio GmbH
Release2020 (2020)
Stable release
2026.06.1 / June 11, 2026; 16 days ago (2026-06-11)
Written inC++ (core), PHP, Python, JavaScript
Operating systemLinux
TypeGroupware, mail server
LicenseAGPL-3.0
Websitegrommunio.com

grommunio is an open-source groupware and email server developed by the Austrian company grommunio GmbH, which is based in Vienna.[1][2] It re-implements the messaging protocols used by Microsoft Exchange Server—among them MAPI over HTTP, Exchange Web Services and Exchange ActiveSync—so that clients such as Microsoft Outlook can connect to it without additional plug-ins or middleware.[3][4] Independent reviewers, and the project itself, describe it as a drop-in replacement for Microsoft Exchange and as an alternative to proprietary platforms such as Microsoft 365 and Google Workspace.[5][2][6][7]

The software is built around a C++ server engine called Gromox, which the project wrote from scratch to speak Exchange protocols natively, and it bundles a web interface together with modules for chat, video conferencing, file sharing, document editing and email archiving.[5][8] grommunio is released mainly under the GNU Affero General Public License version 3, with its source code developed in the open on GitHub.[9][10] Conceptually it continues the line of Linux-based, MAPI-compatible groupware servers that began with Zarafa and Kopano, and Gromox can import data directly from those products.[5][11]

History

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The developing company was entered in the Austrian commercial register (Firmenbuch) in Vienna on 14 August 2020, initially under the name grammm GmbH; its registered office is in the DC Tower in Vienna's Donau City, and Norbert Lambing is recorded as managing director.[1] The product was first introduced publicly in late 2020 as a groupware server and client with a look and feel familiar to Exchange and Outlook users, and the project renamed itself from grammm to grommunio at the end of July 2021.[2][7]

According to an independent review in ADMIN Magazine, the project's developers spent more than four years studying Microsoft's Open Specifications—more than 130 documents totalling several thousand pages—in order to re-implement over 50 protocols and APIs of the Exchange stack in the Gromox engine.[6] The software is updated on a rolling, date-based release schedule.[12]

Architecture

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The central server component is Gromox, written predominantly in C++ and licensed under AGPL-3.0; the project describes it as "capable of serving as a drop-in replacement for Microsoft Exchange".[5][13] Gromox is modular: a front-end http daemon parses HTTP and MSRPC traffic and dispatches it to handler libraries, including exchange_emsmdb for the EMSMDB remote-operations protocol used by Outlook, exchange_nsp for the Name Service Provider Interface (address book), an ews handler for Exchange Web Services, and mh_emsmdb/mh_nsp handlers that wrap those requests inside MAPI over HTTP.[14][5]

The mailbox store is provided by a component named exmdb_provider: each mailbox is kept in its own SQLite database file, accessed through a custom wire protocol so that stores can be served locally or remotely.[15][13] Central user, authentication and configuration metadata are held in a MySQL/MariaDB database, while Redis is used for caching and shared session state.[14][13] Further daemons handle PHP-MAPI bridging (zcore), message indexing for IMAP and POP3 (midb), the IMAP and POP3 services themselves, local mail delivery, change notifications and scheduled tasks.[14] The platform integrates established infrastructure software, using Postfix as its message transfer agent and nginx as a reverse proxy, and it can delegate authentication to LDAP or to a Keycloak-based OpenID Connect/SAML identity provider.[13][6]

On the server side, grommunio supports MAPI/HTTP, RPC over HTTP, EWS, Exchange ActiveSync, IMAP, POP3, SMTP, CalDAV, CardDAV, the Offline Address Book and Autodiscover/autoconfiguration.[13][6] Outlook for Windows connects natively over MAPI/HTTP and RPC over HTTP, configured the same way as against Exchange and without installing client-side MAPI extensions.[3][4] For high availability, grommunio's stateless services can be scaled horizontally behind standard load balancers, with automatic failover provided by the Corosync and Pacemaker cluster stack, and it supports multi-tenancy with delegated administration.[16][4]

Components

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grommunio is distributed as a suite of components. Several are developed by the project itself, while others are forks of established open-source applications with added authentication and integration:[8][6]

The suite is also packaged as the grommunio Appliance, a ready-to-run software image based on openSUSE Leap; it is offered as an ISO, as virtual appliance images and Docker containers, and as a community Raspberry Pi image.[21][8]

Licensing and editions

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grommunio's server components are released under the GNU Affero General Public License version 3; The source code is hosted at the grommunio organization on GitHub, with repositories including gromox, grommunio-web, admin-api, admin-web and grommunio-sync.[10][5]

The software is offered as a free, self-supported community version—limited to a small number of users and intended for evaluation or small installations—and as paid commercial subscriptions that add manufacturer support, service-level agreements and certain enterprise components; according to the vendor, the commercial subscriptions are sold exclusively through certified partners.[22][6] Pre-built RPM and DEB packages are provided for manual installation on enterprise Linux distributions including openSUSE Leap and SUSE Linux Enterprise Server and compatible distributions, Debian and Ubuntu.[23]

Interoperability and migration

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In addition to native Outlook support, grommunio's implementation of Exchange Web Services—which the project reports left beta status and became fully supported in version 2023.11.3—allows Outlook for Mac, Apple Mail, Apple Calendar and GNOME Evolution to connect, while mobile devices synchronise over Exchange ActiveSync through grommunio Sync.[24][17] Automatic client configuration is handled by an Autodiscover service built into Gromox.[4]

For migration, Gromox ships command-line tools that import PST and OST files exported from Microsoft Exchange (chaining gromox-pff2mt into gromox-import), together with a PowerShell script for bulk export from Exchange.[25] Data can also be migrated directly from Kopano and Zarafa installations by reading their SQL databases with gromox-kdb2mt, and from arbitrary IMAP servers mailbox by mailbox.[11][5] Gromox additionally imports the EML, ICAL, VCF, TNEF and MSG formats.[5]

Gromox is one of a small number of independent server-side reimplementations of the Messaging Application Programming Interface, providing C++ implementations of both the MAPI/RPC and MAPI-over-HTTP transports used by Outlook.[5][14]

Reception

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The German IT news site heise online covered grommunio in 2021 as a "free alternative to Microsoft Exchange", reporting on its expansion of supported Linux distributions and processor architectures.[7] Writing for Opensource.com the same year, Markus Feilner described grommunio as an open-source groupware server that functions as a drop-in replacement for Exchange and noted that users "will notice little difference among Outlook, Android, and iOS clients".[2] The German trade magazine Linux-Magazin featured it in 2022 as an open-source "drop-in replacement" for Exchange and, in a market comparison, ranked it among open-source groupware alternatives alongside products such as OX App Suite and Nextcloud.[26] In a 2024 review for ADMIN Magazine, Feilner called grommunio "a feature-rich drop-in replacement for Microsoft Exchange", highlighting its native re-implementation of the Exchange protocol stack and what he described as the first open-source implementation of Exchange Web Services.[6]

grommunio has been positioned within European efforts toward digital sovereignty and reducing dependence on US-based cloud providers in the public sector.[2][6] Deutsche Telekom lists grommunio GmbH among the technology partners in an open-source collaboration package aimed at German public administration, offered alongside products from companies such as Univention, Nextcloud and Open-Xchange.[27]

See also

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References

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  1. ^ a b "grommunio GmbH, Wien". North Data. Retrieved 2026-06-16.
  2. ^ a b c d e Feilner, Markus (2021-09-24). "An open source alternative to Microsoft Exchange". Opensource.com. Retrieved 2026-06-16.
  3. ^ a b "Groupware". grommunio Documentation. Retrieved 2026-06-16.
  4. ^ a b c d e f "Features". grommunio. Retrieved 2026-06-16.
  5. ^ a b c d e f g h i "grommunio/gromox: Groupware server backend for the grommunio Distribution". GitHub. Retrieved 2026-06-16.
  6. ^ a b c d e f g h i j k l Feilner, Markus (2024). "A feature-rich drop-in replacement for Microsoft Exchange". ADMIN Magazine. Retrieved 2026-06-16.
  7. ^ a b c Förster, Moritz (2021-08-13). "grommunio, früher grammm: Neues Release der freien Exchange-Alternative". heise online (in German). Retrieved 2026-06-16.
  8. ^ a b c d e f g h i j "Introduction". grommunio Administrator Documentation. Retrieved 2026-06-16.
  9. ^ "gromox/LICENSE.txt". GitHub. Retrieved 2026-06-16.
  10. ^ a b c d "grommunio (GitHub organization)". GitHub. Retrieved 2026-06-16.
  11. ^ a b "Migration from Kopano". grommunio Migration Documentation. Retrieved 2026-06-16.
  12. ^ "Release Notes". grommunio Administrator Documentation. Retrieved 2026-06-16.
  13. ^ a b c d e "Technology". grommunio. Retrieved 2026-06-16.
  14. ^ a b c d "gromox(7)". grommunio Documentation. Retrieved 2026-06-16.
  15. ^ "exmdb_provider(4gx)". grommunio Documentation. Retrieved 2026-06-16.
  16. ^ "Architecture". grommunio Administrator Documentation. Retrieved 2026-06-16.
  17. ^ a b "grommunio/grommunio-sync: EAS (Exchange ActiveSync) interface for grommunio". GitHub. Retrieved 2026-06-16.
  18. ^ "grommunio/grommunio-dav: CalDAV and CardDAV interface for grommunio". GitHub. Retrieved 2026-06-16.
  19. ^ "Archive". grommunio. Retrieved 2026-06-16.
  20. ^ "Antispam". grommunio Documentation. Retrieved 2026-06-16.
  21. ^ "Guided Installation (grommunio Appliance)". grommunio Administrator Documentation. Retrieved 2026-06-16.
  22. ^ "Pricing". grommunio. Retrieved 2026-06-16.
  23. ^ "Manual installation". grommunio Administrator Documentation. Retrieved 2026-06-16.
  24. ^ "grommunio's Exchange Web Services with Linux clients". grommunio. Retrieved 2026-06-16.
  25. ^ "Migration from Microsoft Exchange". grommunio Migration Documentation. Retrieved 2026-06-16.
  26. ^ Feilner, Markus (2022). "grommunio: Quelloffener Drop-in-Ersatz für Microsoft Exchange". Linux-Magazin (in German). No. 02/2022. Retrieved 2026-06-16.
  27. ^ "Bürgermeister setzen auf Software des Vertrauens". Deutsche Telekom (in German). 2023-09-12. Retrieved 2026-06-16.
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Category:2020 software Category:Groupware Category:Free groupware Category:Email server software Category:Free email software Category:Free software programmed in C++ Category:Software using the GNU AGPL license Category:Collaborative software Category:Linux software

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