Outlook Classic no longer starts on Windows Terminal Server (Feb. 2025)

[German]Once again, I would like to address a topic that was brought to my attention by a blog reader. In his environment, he has noticed that customers can no longer start their Outlook Classic on Microsoft Terminal Server. Perhaps the swarm intelligence of the readership will help.

A reader report about Outlook crashes

German blog reader Bernd D. contacted me in a private message on Facebook at the end of February 2025 and reported problems with Outlook Classic. Specifically, the reader had been experiencing the problem "for several weeks" that Outlook Classic was no longer starting for more and more of his customers on the terminal server, and in some cases locally. These are exclusively customers with Outlook Classic. The new Outlook app, on the other hand, starts without any problems.

Unfortunately, the reader did not mention the Microsoft Outlook build or the Windows Server version on which Terminal Server is running. However, he does state that this problem does not always occur. Therefore, he was unfortunately unable to reproduce it in a joint Microsoft remote maintenance session.

Reinstallations of Microsoft Outlook, etc. have also not been successful for those affected. The reader has already opened a support case with Microsoft, but Redmond announced that it would support these cases for 370 € / hour – and to date there is no solution.

More reports on this issue?

I did a quick search on the Internet to see if anything is known about the above problem. Over the last few weeks, I've had a few posts on Outlook problems here in the blog (see also links at the end of the article) – but nothing specific to terminal servers.

Microsoft has published the support article Classic Outlook and Microsoft 365 applications crashing on Windows Server 2016 dated January 17, 2025, which states that Microsoft 365 applications on Windows Server 2016 can crash after updating to version 2412 (build 18324.20168) or version 2412 (build 18324.20190).

This can be checked in the Windows Event Viewer in the application log. Event entries with the ID 1000 or 1001 with reference to Microsoft 365 applications such as Outlook should be found there. However, the problem should be resolved with version 2412 (build 18324.20194).

I have not found anything in the list of known issues in Outlook apart from the Windows Server 2016 support post above. As of February 11, 2025, someone in the Spiceworks community posted the entry Outlook 2016 on RDS "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed". Updates were installed on an RDS server with Windows Server 2019 and Office 2016 and then the users could no longer start Microsoft Outlook. But at least there is an error message, which is not the case in the reader's error image above.

On reddit.com there is the post Microsoft Outlook not starting Error on Terminalserver Win 2022 (Hybrid Join) from February 2025, which describes a similar error pattern. In a reply, a user notes that he has seen reports where deactivating ADAL and WAM for authentication has solved the problem. However, Microsoft advises against deactivating them in this article.