Microsoft 365 outage hits Outlook email and Teams calendars worldwide

A widespread Microsoft 365 outage began on Thursday, disrupting Outlook email and Teams calendar features across the globe. The issue persisted into Friday, affecting government email systems and Microsoft 365 connectors for AI assistants like ChatGPT and Claude. Microsoft acknowledged the problem in a 7:25 am UTC update, stating that a recent patch had improved stability on some servers but there was no timetable for a full restoration.

The root cause was an overloaded process handling secure connections, which caused affected servers to stop processing requests. Microsoft attempted to mitigate the issue by restarting infrastructure, redirecting network traffic, and expanding server capacity. The outage did not appear to result from a security breach. Additional features within Microsoft Copilot and Defender for Office 365 were also impacted.

Teams users encountered difficulties scheduling meetings and sending invitations, though most calls and chats remained functional. Microsoft 365, utilized by numerous businesses and government agencies worldwide, hosts mailboxes and calendars on Exchange Online, which is essential for outside apps accessing user data. OpenAI and Anthropic reported errors in their respective AI assistant connectors due to the outage.

High-profile users, including the US Court of Appeals for the Tenth Circuit and Japan's Finance Ministry, experienced significant disruptions, with some services out of reach for parts of the day.