Teams – You can now control the login pre-fill to sign-in to Teams

— Microsoft Teams

If you organization uses a different UPN for cloud and on-premises access, you can now control how Teams is going to pre-fill the sign-in page for your users when the device is domain joined.

The following registry ley is going to tell Microsoft Teams to not pre-fill the username with the UPN from Active Directory.

Key: Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\Teams
DWORD Value: SkipUpnPrefill
Value: 0x00000001 (1)

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