Fix authentication issue in Outlook for Mac when connecting to an Office 365 Plan1 service

Symptoms

Authentication automatically fails and Outlook may require a password without any interaction. You may see the following sign-in prompt.

Cause

The authentication issue occurs when Outlook is trying to connect to Teams to retrieve your free/busy status, but you don't have a Teams license. This only happens with a Microsoft365 P1 license.

Resolution

To fix this issue, follow the below steps to execute a Terminal command.

1. Quit Outlook.

2. Launch Terminal on your Mac by doing either of the following:

   • Click the Launchpad icon in the Dock, type "Terminal" in the search field, then click Terminal.
     
     

   • In the Finder, open the /Applications/Utilities folder, then double-click Terminal.
     
     

3. In the Terminal window, enter “defaults write com.microsoft.Outlook ClassicCalendarDisableMsTeamsMeeting -int 1” (without quotes).
   
   

4. Press Enter.