Open Source Back-End Services: A Migration Guide for Directory, Storage, Mail, and Real-Time Communication¶

Stefane Fermigier (Abilian) · sf@abilian.com

Draft working paper v1.0, 2026-08-30. Guide 1 of 2. The companion volume, The Open Source Workstation: A Migration Guide for Applications, the Desktop, and the Managed Linux Estate, covers end-user applications and the managed Linux desktop. Product statuses are stated as of the date given in §1.4; entries marked † were moving at that date and need re-checking before a procurement decision.

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Abstract¶

This guide addresses a question that most organisations now face in some form: what would it take to run the collaboration back end (directory, file services, mail and calendar, document collaboration, and real-time communication) on open source software, and what does that cost. It adapts three public studies, two commissioned by the Swiss Federal Chancellery in 2024 and one by the German state of Schleswig-Holstein in 2022, from their original public-administration setting to organisations generally, and updates their product assessments.

The guide departs from its sources in three ways. It treats supplier depth as a first-class selection criterion alongside function and maturity, because a single-vendor product replaces the identity of a dependency without changing its structure, and because only a plural supplier base turns an open licence into an actual ability to change your mind. It separates directory of record, authentication, and device policy into three procurement decisions instead of looking for one product that covers all three. And it treats exit cost rather than licence cost as the object, following the Schleswig-Holstein strategy's observation that the cost of client access licences is best understood as the price of a dependency.

It also covers what the source studies leave out, which is most of the engineering. Product selection occupies §§4 to 11, including the AI assistance question that postdates every source here and that supplies the mechanism behind the price escalation the economics rest on. §12 takes the hosting decision, on which most of the sovereignty turns and which a guide discussing only software would miss. The work then occupies §§13 to 19: reference architectures and sizing, data-migration mechanics, coexistence patterns, backup and continuity, security baselines, operations, and what to put in a contract. A migration fails in those chapters, and succeeds in them.

The headline finding is uncomfortable for both the enthusiast and the sceptic. Credible open-source options now exist in every domain examined, and in two of them (groupware with native Outlook compatibility, and integrated sovereign suites) the position improved materially after the source studies were written. No source in the corpus supports a claim of cost savings, and the most rigorous of them concludes cost parity over a long horizon. The case for migrating rests on exit cost, price-escalation exposure, and optionality, all of which are real and none of which is a discount.

JEL: L86, L17, M15, D23, L15.

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Cite this paper¶

Fermigier, S. (2026). Open Source Back-End Services: A Migration Guide for Directory, Storage, Mail, and Real-Time Communication.
Report v1.0, Abilian Econ Lab.
https://econ.lab.abilian.com/papers/backend-services/