Microsoft has confirmed a new bug affecting the classic version of Outlook for Windows that causes email synchronization to silently break for users who connect their Gmail or Yahoo Mail accounts. Rather than displaying a login prompt when credentials become invalid, the application simply stops syncing — often leaving users unaware that their inbox is no longer updating.

Microsoft officially documented the issue on its support pages, noting that the problem is confirmed to arise after a password change on the Gmail or Yahoo side. However, the company added that other, as-yet-unidentified circumstances may also trigger the same failure, and that investigation is ongoing.

What Users Are Seeing

When the bug occurs, affected users encounter a series of error codes in the Outlook Send/Receive dialog. The errors give little actionable guidance, and no re-authentication prompt appears. The three error conditions Microsoft has documented are:

The core problem is an authentication breakdown: when a password changes, Outlook’s stored identity credentials become stale. Normally, the application would detect this and prompt the user to sign in again. In the affected configurations, that re-authentication prompt never appears, leaving the account in a broken state with no clear indication of why.

“There might be other circumstances that lead to this same issue that we are investigating.”

— Microsoft Support Documentation, March 9, 2026

Who Is Affected

The issue applies specifically to the classic Outlook for Windows desktop application — distinct from the newer “New Outlook” experience Microsoft has been rolling out. Users who have linked a personal Gmail or Yahoo Mail account to their classic Outlook profile are potentially at risk, particularly if they recently updated their email password through those providers’ websites or apps.

The bug does not appear to affect Microsoft’s own email domains (Outlook.com, Hotmail, Live), nor does it impact the new Outlook application or the web version of Outlook.

Temporary Workaround: Registry Edit

While a permanent fix is not yet available, Microsoft has published a manual workaround that clears the stale identity data from the Windows Registry, forcing Outlook to request fresh credentials on next launch. The steps are as follows:

1. Right-click the Windows Start Button and select Run. Type Regedit and click OK to open the Registry Editor.
2. In the Registry Editor address bar, paste the following path and press Enter:
   Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities
3. Under the Identities key, expand each sub-key in the left panel until you find the one that displays the email address of the account that is no longer syncing.
4. Delete that specific sub-key (right-click → Delete). Do not delete any unrelated keys.
5. Close Registry Editor, then restart classic Outlook. You will be prompted to sign in to the affected account. Once you sign in, synchronization should resume normally.

Microsoft notes that this workaround resolves the immediate issue for the affected account, but it does not prevent the underlying bug from recurring. If the password is changed again, the same steps may need to be repeated until a proper fix is issued.

Microsoft’s Response

The issue was formally acknowledged by Microsoft on March 9, 2026, and is currently listed under the “Investigating” status on the official Classic Outlook for Windows known issues page. The company has stated that it will update its support documentation with fix status information as soon as it becomes available.

Microsoft has not provided an estimated timeline for a resolution, nor has it confirmed whether the fix will be delivered as part of a scheduled Office update or as an out-of-band patch.

What You Should Do Now

If you use classic Outlook with a connected Gmail or Yahoo Mail account and have recently changed your password on either service, check whether your mail is still syncing. The absence of a re-authentication prompt means the failure can go unnoticed for an extended period. If you are experiencing the error codes described above, apply the registry workaround above to restore synchronization while awaiting Microsoft’s official fix.

Users who have not yet changed their passwords but are concerned about this issue may want to defer password changes until a patch is released, or consider temporarily using the Gmail or Yahoo web interfaces to access their mail.