Microsoft Outlook/365 still down after 12 hours

Microsoft 365 reported a widespread connectivity incident affecting access to Exchange Online mailboxes through multiple connection methods. The disruption was first reported in the Americas but was later confirmed as potentially affecting users in any region. Microsoft identified elevated load across several regions and traced it not to a surge in demand, but to servers becoming unexpectedly unavailable, which strained the infrastructure still operating. The investigation also pointed to failures in a component responsible for checking server health, while an overwhelmed core process was causing some affected servers to lose capacity.

Across roughly 12 hours, Microsoft paused deployments, shifted traffic to other infrastructure, restarted affected servers, and tested alternative health checks and configuration changes. Some servers returned to service and recovery was briefly observed, but restored servers became unresponsive again when they received traffic. Microsoft then limited some traffic to affected systems and analyzed diagnostic data, but its latest update said the changes intended to improve serviceability were not working as expected. The company was seeking alternative ways to increase capacity amid persistent traffic-management imbalances. Updates were available under incident IDs EX1550543 and MO1550821 in the Microsoft 365 admin center, or through Microsoft’s public service-status site if the admin center could not be accessed.