Dutch tax agency abandons its Microsoft 365 rollout after 5,000 of 47,500 staff had moved

About one in ten Belastingdienst staff were already on Microsoft 365. In 2027 their mailboxes and calendars move a second time, onto servers the agency runs itself ^[19][6]. The other 42,500 or so make the move once ^[20].

"This allows us to work in a focused way towards a sustainable and more autonomous solution for these functions," Eerenberg wrote, in TNW's translation from Dutch ^[10]. It starts as a mail and calendar project, and the agency will reuse existing licences where it can to hold down extra spending ^[14]. Neither report puts a cost on the move.

The review board's headline finding was that the agency's approach would not lead to a suitable workplace ^[5]. Its control findings come in two kinds. The agency did not use Double Key Encryption, a feature that would have given it more control over its data, and end-to-end encryption was off by default for one-to-one Teams calls ^[12]. Both of those describe how the agency had set up Microsoft 365. Lock-in and the missing exit plan are different. They describe the whole arrangement, and the board said they limited the agency's freedom to pick a more sovereign option later ^[13].

According to TechRepublic, the agency chose Microsoft 365 in the first place because suitable alternatives appeared to be unavailable ^[8]. Within a year its own building work changed that answer. Eerenberg wrote that the on-premises route is possible partly because the agency added data centre capacity ^[7]. That backs the idea that running your own servers is workable again, but only for an organisation that has already added data centre capacity. The Dutch case does not show it for one that has not. TechRepublic says the open question is whether the replacement systems can match the reliability, security and scale of the existing setup ^[21].

So far the costs show up as missing features and later dates. Several records-management features came bundled with Microsoft 365 and do not exist on-premises, so some archive tools are delayed while the agency works out replacements ^[15]. The agency also took hosting of its new VAT system back from the supplier. As a result the VAT refund system now goes live in April 2027, and the domestic VAT rollout has moved from 1 July 2027 to the third quarter ^[16]. Microsoft declined to comment to The Register ^[17].

The board advised looking at alternatives one function at a time ^[14]. Its findings sort each function along two lines: whether the control gap is a setting or a dependency, and whether the capacity to run that function in-house already exists. If the gap is a setting and there is no spare capacity, the fix belongs inside the current suite. Spare capacity does not change that answer for a setting gap, because leaving means giving up bundled features like the Dutch records tools ^[15]. A dependency with no capacity behind it needs a written exit plan for each function before anyone orders hardware. The fourth case, a dependency with the capacity already built, is where the Dutch tax agency sits ^[7]. The job there is to list the bundled features that will not exist on-premises and the dates that will slip ^[15][16].