I wanted to disable the prompt and button for new Outlook. I found this guide and wrote a few lines of PowerShell to automate it and wanted to share.

# Source https://edi.wang/post/2025/1/20/how-to-stop-automatically-switching-to-new-outlook
$path='HKCU:\Software\Microsoft\Office\16.0\Outlook'

# Remove and create to ensure correct data type
Remove-ItemProperty -Path "$path\Options\General" -Name 'NewOutlookAutoMigrationStage' -ErrorAction SilentlyContinue
New-ItemProperty -Path "$path\Options\General" -Name 'NewOutlookAutoMigrationStage' -Type DWord -Value 1
Remove-ItemProperty -Path "$path\Options\General" -Name 'NewOutlookAutoMigrationStage'
Remove-ItemProperty -Path "$path\Options\General" -Name 'NewOutlookAutoMigrationType'
Remove-Item -Path "$path\NewOutlook"
# Remove and create to ensure correct data type
Remove-ItemProperty -Path "$path\Preferences" -Name 'UseNewOutlook' -ErrorAction SilentlyContinue
New-ItemProperty -Path "$path\Preferences" -Name 'UseNewOutlook' -Type DWord -Value 0
Remove-ItemProperty -Path "$path\Preferences" -Name 'NewOutlookRenudgeStartDate'
Remove-ItemProperty -Path "$path\Preferences" -Name 'NewOutlookRenudgeStartDate'

Nice. So this is all user-based though?

You could do a machine deployment with something like PSADT but it's probably overcooking it (I don't really understand when/how it switches from old to new)

Does this work different than the policy key? As far as I know the keys under software\policies are used by both group policy and intune, and honored by windows home editions so I'd expect they'd work more reliably than an outlook config setting.

Good stuff!

As far as I know, group policy changes the registry behind the scenes. I base this only on reading about how to do stuff were there was usually a group policy and reg solution. Anyway, my work computer is not managed so I have to do this stuff myself and I had to setup everything twice (fresh from repair and then I had to reinstall Windows because I messed up the WiFI driver) recently. The new outlook stuff annoyed me so I figured I could do the registry changes as a PowerShell script and share it here.

So this is all user-based though?

I would assume so since it is HKEY_CURRENT_USER. I took a glance at HKEY_LOCAL_MACHINE and the same keys were not there. Perhaps this would had to be run for each user at first login.

I am the only user of my work computer and it is not even managed, so PSADT would indeed be overkill. :-)

Yes, indeed!

edit but, you know, don't let that stop you from really fixing it (so hard that it might need some additional remediation afterwards)

Yes, looks to be different registry keys. The Outlook ADMX Template has the settings:

Which should hide the toggle and turn off Microsoft's forced change.