Microsoft has fixed a known issue that stopped Gmail and Yahoo accounts from syncing in classic Outlook, which produced 0x800CCC0F and 0x80070057 errors. Some customers may still see sync problems until their OAuth token expires or can force a sign-in using Microsoft’s registry workaround while Microsoft continues investigating related classic Outlook issues such as EWS group connection errors, a disappearing mouse pointer, and a Teams Meeting Add-in conflict. #Outlook #Microsoft365
Keypoints
- Microsoft resolved the Gmail and Yahoo sync bug that caused 0x800CCC0F and 0x80070057 errors in classic Outlook.
- Syncing for affected accounts stopped on February 26, 2026, and users were not prompted to sign in when sync failed.
- The fix was deployed in Microsoft 365, but some customers may need to wait for OAuth tokens to expire (about one hour) to regain sync.
- A temporary workaround forces a sign-in by deleting identity entries under ComputerHKEY_CURRENT_USERSoftwareMicrosoftOffice16.0CommonIdentityIdentities in the Windows Registry Editor.
- Microsoft is also investigating other classic Outlook problems—including EWS-related “Can’t connect to the server” errors, a disappearing mouse pointer, and a Teams Meeting Add-in issue—and requests diagnostic logs via a Microsoft 365 admin support case.