Dutch tax office drops Microsoft 365 for on-premises and open source

Dutch tax office drops Microsoft 365 for on-premises and open source

5 October 2026: The Dutch Tax and Customs Administration, the Belastingdienst, has dropped its plan to run its office environment on Microsoft 365 and will host the replacement on servers it controls, combined with open source software. State Secretary for Finance Eelco Eerenberg set this out in a letter to the House of Representatives. Tax, customs and the benefits service (Toeslagen) are all covered.

The 2025 choice of Microsoft 365 had already been reopened earlier this year. In the letter the State Secretary says the on-premises route is possible partly because the administration has managed to expand its data centre capacity. He describes the on-premises scenario as software running on servers of the Belastingdienst or servers it controls.

The letter gives a sequence. Mail and calendar come first, delivered on-premises in 2027. European open source tools for personal storage and collaboration follow later in 2027 and in 2028. The approach is built to reuse existing licences wherever possible, so that extra investment stays low. The letter also follows advice from the Dutch Advisory Council on ICT Assessment (Adviescollege ICT-Toetsing) not to rely on one solution from one supplier, and to examine alternatives for each function separately.

There is a cost to the switch. Some of the planned tools for records management were part of the Microsoft 365 package and are not available on-premises. The Belastingdienst is working out what it needs to close that gap, and the State Secretary says he will report back no later than the next progress letter.

The Register adds detail the letter does not carry. It reports that the rollout had reached about 5,000 of 47,500 employees by June, and that the advisory council had criticised the design on information security, including the use of standard Microsoft encryption rather than Double Key Encryption, and the lack of end-to-end encryption for group Teams calls. It also reports that the council raised vendor lock-in and the absence of an exit strategy. Microsoft declined to comment, according to the outlet. The Register quotes the chief executives of Element and Nextcloud welcoming the decision.

For suppliers to Dutch public bodies, the letter is a specific signal: mail and calendar hosting, then file storage and collaboration, are the functions being re-sourced, and archive and document management are an open requirement. The administration's roadmap is due to parliament in the first quarter of 2027.

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Sources

• Kamerbrief Toekomstbestendigheid Belastingdienst, State Secretary for Finance E. Eerenberg, Tweede Kamer (ref. 2026Z21114), 5 October 2026
• The Register: Dutch tax office ditches Microsoft 365 cloud for on-premises alternative, 7 October 2026