Turning Off “New Outlook” in Outlook 16.58

SpamSieve
#1

There’s a bug in Outlook for Mac 16.58 where the switch to turn off New Outlook is missing. This is especially a problem because at launch it encourages users to opt into the New Look without telling which features (including some required by SpamSieve) will be lost by doing so. The release notes claim that the switch has been restored, but I found that even in the 16.59 beta the switch is still gone. You can, however, turn off New Outlook by entering this command in Terminal:

defaults write com.microsoft.Outlook IsRunningNewOutlook NO

and then restarting the app.

Outlook 16.7 changes
#2

This Terminal command also works in Outlook 16.7, if you have a Microsoft 365 subscription. The new free version only works in “New Outlook” mode.