grommunio

grommunio is a groupware platform made by grommunio GmbH in Vienna, Austria. It covers email, shared calendars and scheduling, contacts and global address lists, tasks and notes, chat and video meetings, and file sharing with online editing. The company presents it as a replacement for an on-premises Microsoft Exchange server, which organisations run on their own servers, in a private cloud or through a certified hosting partner.

What it does

The server, gromox, speaks the protocols Outlook and mobile phones use with Exchange: MAPI over HTTP, RPC over HTTP, Exchange Web Services and Exchange ActiveSync. It also supports IMAP, POP3 and SMTP for other mail clients, and reads users from LDAP or Active Directory. Its repository lists import from PST, OST and MSG files and from Zarafa and Kopano servers, which helps when moving mailboxes from an older system. grommunio provides a web interface and native clients for Linux, Windows, Apple devices and Android.

Who it is for

It suits organisations that want Exchange-style email and calendars without a Microsoft cloud subscription, such as public bodies, schools and businesses with rules on where data is stored. The company names deployments from 6 to more than 100,000 users. It says it holds no customer data itself, and that GDPR compliance depends on how and where each organisation deploys it.

Pricing and editions

The software is open source on GitHub and Codeberg. On 27 October 2026 the Community edition was free for up to five users without manufacturer support. Paid subscriptions were Basic at 1.99 euros, Plus at 3.99 euros and Business at 5.49 euros per user per month, starting at 6, 6 and 50 users; Enterprise starts at 1,000 users on a negotiated price. Every plan includes all features, and licences are sold only through certified partners.