[English]A quick update and a question about whether anyone else is affected. A reader informed me that he has recently been receiving an increasing number of reports from customers about Microsoft 365 outages. Microsoft appears not to have renewed a certificate that has expired. At least, that's what the error messages suggest. Microsoft has confirmed at least one outage under EX1464935.
A Reader Report on M365 Issues
Blog reader Michael ontacted me via email on August 31, 2026, at around 7:05 p.m. (CET), because his customers were reporting M365 issues. Michael wrote:
IFor the past hour, I've been receiving calls for help from customers whose Outlook can no longer connect to Microsoft 365 Exchange Online. Logging in via webmail (outlook.office.com) isn't working either. Error message: "something went wrong"
The reader wrote that he had tried to view the relevant tenants via the Partner Center. However, only limited information about the mailboxes is displayed there. For example, information on mailbox size and used storage is missing. If he tries to make a change in the tenant, the following error appears:
Exchange: The execution of cmdlet failed. {"error":{"code":"InternalServerError","message":"Internal server error","innererror":{"message":"Internal server error","type":"Microsoft.Exchange.Admin.OData.Core.ODataServiceException","stacktrace":"","internalexception":{"message":"The cert with thumbprint 19F04B8A233DD9CE916F118056D224A1751729EA is expired.","type":"Microsoft.M365.Security.CredSMART.M365SecretException","stacktrace":""}},adminapi.warnings@odata[.]type:"#Collection(String)","@adminap[i].warnings":[]}} Translate.https://g.microsoftonline.com/0BX20de/510;
Michael wrote: "It looks like an internal certificate at Microsoft has expired," referring to the error message above. The reader notes that he checked X—there's a tweet where Microsoft confirms the issues:
We're investigating reports of Exchange Online issues. Please see EX1464935 in the admin center for more information.
According to a reader, the Admin Center is completely inaccessible for some of these tenants. Within my German blog post, a reader postet a script to see which mailboxes are affected in the tenant. Is anyone else among our readers affected by this outage? Bleeping Computer has also reported on the outage, and they list OpenAI as being affected as well.
