Microsoft fixes classic Outlook failure that prevented Gmail and Yahoo synchronizing and explains the expiry of tokens OAuth

Microsoft has finally corrected a failure that was preventing the Gmail and Yahoo accounts from synchronizing with the classic Outlook version. The problem was shown by error codes as 0x800CCC0F and 0x80070057, and many users saw how their mail stopped updating without receiving any notice to relog in.

According to the company, the interruption began to be noticed on February 26, 2026: in many cases Outlook stopped asking for credentials when the synchronization failed, leaving the entry trays unupdated until the problem was solved in the service. Microsoft posted a support note explaining the causes and steps to recover the connection; you can see that statement directly on the Microsoft support page here: Users get errors 0x800CCC0e / 0x800CCC0F when synchronizing Gmail and Yahoo accounts in classic Outlook.

Microsoft indicates that the correction was deployed in the Microsoft 365 service, but that some customers could continue to experience problems until the OAuth token associated with your account is over. In simple words, even if the server already accepts connections, the Outlook client can continue to use an old token that prevents automatic reauthentication. Under normal conditions that token expires approximately one hour after a password change, and once it turns out that Outlook should ask you to log back in.

If you don't want to wait, Microsoft shared a temporary solution that forces Outlook to ask for credentials: remove, with great care, the entry corresponding to the affected address within Identity in the Windows Registry. The route involved is Computer\ HKEY _ CURRENT _ USER\ Software\ Microsoft\ Office\ 16.0\ Common\ Identity\ Identity. It is important to stress that touching the record can have consequences if it is done incorrectly, so only use this method if you know what you do or after you back up the record. The supporting document itself includes instructions and warnings on this procedure.

In addition to this failure, Microsoft has recognized other problems that affect the classic version of Outlook. Among them, an error that shows "Can't connect to the server" when creating groups when the tenant has enabled Exchange Web Services; the details of the company's notice are available in this other supporting article: Users may get the error "Can't connect to the server" when creating groups in classic Outlook. There have also been reports of the disappearance of the mouse pointer in classic Outlook and other Microsoft 365 applications, and at the beginning of the year Microsoft solved an incident that prevented the opening of encrypted emails after the December 2025 updates.

To help with the diagnosis, the company has asked affected customers to send the registration files and open a case of support through the Microsoft 365 management center. If you need personalized assistance, the official contact path and the process to open incidents are described in the Microsoft support section: Contact Microsoft support. It may also be useful to understand how OAuth tokens and their life times work; Microsoft offers technical documentation on access tokens that clarifies why a correction on the server is not always reflected immediately in the client: Access tokens in Microsoft identity platform.

If you would like to minimize the impact while the corrections are stabilized, there are practical alternatives: using the Gmail or Yahoo web client, checking that Office and Windows are up-to-date, and closing into Outlook to force a new login when possible. For organizations with many users, propose progressive migration to the new Outlook version (Microsoft 365) or strengthen internal support channels can save time and reduce exposure to this type of fault in the classic customer.

In short, the good news is that the incidence in the service is already fixed, but the complete recovery may take a little longer on some teams because of the validity of the authentication tokens. If your mail remains unsynchronized, wait an hour after any password change, try to close and reopen, and if it persists, contact with support or value the temporary solution of the registry with caution. Maintaining up-to-date systems and preparing support channels for these scenarios remains the best strategy to minimize interruptions.