Prevent migration from Classic Outlook to New Outlook

[German]Microsoft plans to switch certain Microsoft 365 user groups from Outlook Classic to the new Outlook app from the beginning of 2025. Some people has developed remediation solutions to prevent this. Here is a solution I came across yesterday.

PowerShell and Intune as a solution

I had mentioned the facts surrounding Microsoft's plans to migrate users of a Microsoft 365 Business Standard and Premium license to the new Outlook for Windows from 6 January 2025 in the blog post Migration from Outlook Classic to New Outlook starts for business customers at the beginning of 2025 at the beginning of 2025, also for business customers. A discussion arose there about how administrators can prevent this changeover using GPOs.

At the beginning of December 2024, the following tweet drew my attention to the fact that some administrators are probably dealing with the question "How can I prevent clients from switching to the new Outlook".

In this article, Martin Bengtsson, an ex-Microsoft MVP from Denmark, deals specifically with the question of how he can prevent his users from migrating or switching to the new Outlook app using PowerShell and Intune.

In his PowerShell scripts, he checks a registry entry to prevent switching and sets this entry if necessary. He then uses Microsoft Intune to distribute and execute these PowerShell scripts on the clients.

My comments

The concept presented in this article stand or fall on the assumption that Microsoft will continue to evaluate the registration entry for blocking a migration in the future. There is a good chance that the lock will "last" even longer when switching from classic Outlook to the new Outlook app. But I won't put my money on it.

With regard to the replacement of the mail and calendar app from Windows by the new Outlook app (see also Trouble with the new Outlook app: forced update and sluggish behavior?), the above scripts are useless in my opinion. The Mail and Calendar app is dead at the end of December 2024 and does not take the above registration entries into account.