Microsoft 365 Outage Hits Customers Due to Expired Certificate
A Microsoft 365 outage affected customers on August 31, 2026, due to an expired certificate. According to a reader's report, several customers experienced issues with Outlook and webmail connections, displaying error messages that pointed to an internal server issue.
The error message revealed that the cert with thumbprint 19F04B8A233DD9CE916F118056D224A1751729EA was expired. A reader confirmed this by trying to view the relevant tenants via the Partner Center, where only limited information about mailboxes was displayed, and attempting to make a change resulted in an internal server error.
Microsoft acknowledged the issue under EX1464935 and stated that they were investigating reports of Exchange Online issues. The company also confirmed that Teams, SharePoint, and Defender XDR were affected. A remediation strategy had been developed to address the issue, which was being applied to a portion of infrastructure for testing.