Microsoft has resolved an issue that was causing synchronization problems between classic Outlook and Gmail or Yahoo accounts, according to an update in the company’s support documentation. The issue affected Microsoft 365 users and started on February 26, 2026. The bug prevented affected accounts from syncing and resulted in error codes 0x800CCC0F and 0x80070057.
Outlook Sync Issue Resolved, But Delays May Persist
Microsoft reports that the issue has been resolved on the Microsoft 365 service as of Friday. However, some users may still experience temporary problems due to the way authentication tokens behave.
The company notes that Outlook may not prompt users to sign in again immediately after the fix. Syncing will resume once the OAuth token expires, which usually happens about an hour after a password change.
How To Restore Classic Outlook Syncing Faster
Users who prefer not to wait for the token to expire can manually trigger a sign-in prompt using a Microsoft-provided workaround.
To do this, open the Windows Registry Editor, navigate to the relevant location, delete the registry entries for the affected email account, then restart Outlook and sign in again when prompted. Microsoft shared this workaround before deploying the service-side fix.
Other Classic Outlook Problems Microsoft Is Investigating
Microsoft is investigating additional issues affecting the classic Outlook client. One bug may cause errors stating “Can’t connect to the server” when creating groups in environments where Exchange Web Services is enabled.
Another problem impacts Microsoft 365 apps, including Outlook and OneNote, where some users report that the mouse pointer disappears. Microsoft has encouraged affected customers to submit diagnostic logs through a Microsoft 365 admin support case to help with ongoing investigations.
What To Do If Classic Outlook Will Not Sync Gmail Or Yahoo
Users experiencing sync issues should wait for their OAuth token to expire or change their password to initiate a new sign-in. If syncing still does not resume, the registry workaround can be used to force reauthentication.
When The Classic Outlook Sync Fix Reaches Microsoft 365 Users
The fix has already been rolled out to the Microsoft 365 service. Microsoft notes, however, that the full resolution depends on the OAuth token expiration and may take up to an hour to affect affected users.
