grommunio Developer Guide

grommunio GmbH

2026-07-02

grommunio Developer Docs

grommunio is a comprehensive communication and collaboration solution that includes e-mail, calendaring, contacts, tasks, notes, video meetings, chat and file management.

Audience

This document is for developers working with grommunio. It helps to integrate and extend grommunio based on the developers own requirements.

Reference & resources

Admin API referenceThe complete grommunio Admin REST API specification, with request/response schemas and ready-to-copy code samples — generated from the upstream OpenAPI definition.

Gromox internals & specsProtocols, MS-OXO notes, MAPI properties, error codes and the glossary — generated from the upstream gromox/doc sources.

Project setupBuild and developer setup for each grommunio project — Gromox, Web, Sync, DAV, Admin API/Web and Index — from their READMEs.

Gromox wikiCurated pages from the Gromox project wiki: addressing, folder permissions, sync issues, vCard handling and more.

Debugging with FiddlerCapturing and inspecting MAPI/HTTP traffic between clients and grommunio.

Offline reading

This section is also available to download for offline use:

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Fiddler

Fiddler installs itself as a system proxy, i.e. when Fiddler is set to capture traffic, the system proxy setting is changed to point to 127.0.0.1:8888. Therefore, Fiddler is not entirely transparent.

When capture has just been activated, it may take a few HTTPS connection attempts before things actually work. So, if opening a MAPI profile fails, retry a few times.

Be aware that TLS certificate warning dialogs (which are normal under these circumstances) might pop up under other windows and go unnoticed.

The MAPI Inspector for Fiddler does support both EMSMDB and NSP.

Fiddler is not able to deal with RPCH requests at all, and connecting to EXC in this mode will fail. Only MAPIHTTP will work. The EAC Shell command Get-OrganizationConfig and Set-OrganizationConfig -MapiHttpEnabled $true can be used to read/write the setting. A change seems to necessitate a reboot to activate.