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 v1.2, 2026-09-28. Guide 1 of 2. The companion volume (Fermigier 2026a) 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 at what 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. It also draws on two further documents, a French field study of Linux workstation migrations and Schleswig-Holstein's 2024 open-source strategy.

The guide departs from its sources in three ways. It treats supplier depth as a first-class selection criterion alongside function and maturity. A single-vendor product replaces the identity of a dependency without changing its structure; 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. Its object is exit cost, the price of leaving, 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 contract terms. 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 is materially better than the source studies record. No source in the corpus supports a claim of cost savings. 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.

Keywords: open source software, IT migration, public procurement, directory services, email, collaboration, total cost of ownership.

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

Break-even incumbent cost against the evaluation horizon, for three estate profiles, with the incumbent's price flat (solid) or rising at the 8.7% a year buyers report for a locked base (dashed).

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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 v1.2, Abilian Econ Lab.
https://econ.lab.abilian.com/papers/backend-services/