Overview
- A platform-wide failure began on November 12 when Exchange Online connections started failing and user incident reports surged into the tens of thousands.
- Microsoft says the outage was not a cyberattack but followed widespread automated health-check failures that caused many servers to go offline and overload remaining capacity.
- Engineers halted routine updates and configuration changes, restarted affected servers, rerouted traffic and switched to alternate health checks while continuing an internal investigation under incident EX1550543.
- The disruption impaired Outlook, Teams, SharePoint, OneDrive and Copilot and affected connectors used by AI services such as OpenAI and Anthropic, with public monitors showing spikes of roughly 100,000 reports for Outlook and reports from about 74 countries.
- This is Microsoft 365’s third major outage in 2026 and it highlights questions about change management and automated health-check design that could affect enterprise operations and third-party AI integrations as the company completes its root-cause review.