If you're an administrator, you can use the following diagnostic tool to validate that a user has the correct policies to enable the Teams Outlook add-in.
Select the following Run Tests button to populate the diagnostic in the Microsoft 365 admin center:
Run Tests: Teams Add-in Missing in Outlook
In the Username or Email field under Run diagnostic, enter the email address of the user who is experiencing issues when they try to enable the Teams Outlook add-in. Then, select Run Tests.
The tests will return the best next steps to resolve any tenant or policy configuration issues and validate that the user is correctly configured to enable the Teams Outlook add-in.
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