grommunio @ FOSDEM 2024

26. February 2024 | Blog

grommunio @ FOSDEM 2024

At the beginning of February, Jan Engelhardt gave a presentation on grommunio at FOSDEM in Brussels entitled „Implementing 27 MS Exchange Protocols in Open Source“. In the “Modern E-Mail” devroom, he explained the depths, quirks and problems that the developers of grommunio had to overcome in order to create and expand the leading open source replacement for Microsoft Exchange. The dev-room was overcrowded, and Linux Magazine reported on it.

Jan Engelhardt @ Fosdem 2024
At grommunio at FOSDEM 2024, people stood and were not let in. Here is Jan Engelhardt’s jam-packed talk on MSEX protocols. (photo: Markus Feilner, CC-BY 2024)

The annual FOSDEM conference at the Libre Université de Bruxelles (LUB) is the largest and most prestigious open source developer event in Europe. It began more than 20 years ago and today attracts more than 12,000 open source developers, enthusiasts and evangelists to the capital of Europe. The event’s almost 1,000 talks and presentations will be recorded, giving everyone plenty of time to talk, discuss, collaborate and network.

grommunios Lead Software Architect at FOSDEM

This year, grommunio is proud to have been part of the free and open event: Jan Engelhardt, grommunio’s lead developer and software architect, gave a talk on “Exchanging Microsoft: implementing 27 MS Exchange protocols & APIs in OSS with grommunio”.

MAPI, the Messaging Application Programming Interface, is a “somewhat ambiguous term”, says Engelhardt. “It is used for concepts as well as for the data mode, programming interfaces and network protocols on the wire.” Thanks to Microsoft, all documentation is freely available, the specifications amount to “132+ documents on 8400+ pages, in addition to the Internet mail protocols (i.e. RFC 5322, 5545, etc.) that must be supported anyway.” Engelhardt and his team at grommunio dived deep into these documents – and also helped to fix some problems. This is how grommunio became a contributor to the open stack of specifications used by Microsoft and all its customers.

gromox @ Fosdem
Not only did grommunio work through thousands of pages of specifications, but we also contributed by fixing the bugs we found. (slide of the presentation)


No wonder the developer room H.2213 was overcrowded – with grommunio being the first open source groupware ever diving that deep into the forest of MS Exchange protocols. Our latest version even includes the world’s first complete implementation of EWS, Exchange Web Services. The photo of Jan’s presentation even made it into the German Linux-Magazine’s upcoming report on FOSDEM (issue 04/24 will be published in early March), as an example of a crowded, innovative presentation.

Recordings and Slides

For all of you that did not make it into the room and had to stand inline outside the door, here’s

Jan explained in detail which and how many protocols and formats can be found in grommunio today, with a lot of side notes on tools we used, problems we found (e.g. with some binary formats in Exchange) and more. The presentation is about 20 minutes, but it’s full of further information.

If you have technical questions, feel free to contact us or send us an email.