Microsoft identifies likely cause of Nov. 12 Outlook outage

Microsoft has identified a likely cause for the Nov. 12 Outlook outage, citing failed server health checks that took some servers offline and disrupted email access for many users. The company said on X that the failures may stem from a specific component on affected servers, with heavier-than-usual load across multiple regions contributing to connection problems. Microsoft is deploying a targeted change to bypass the component and has taken steps to prevent further server outages. The outage initially affected Exchange Online mailboxes in the Americas, later expanding to potentially impact Microsoft 365 users globally. Nearly 130,000 problem reports appeared on Downdetector, with users facing inbox loading and email sending issues, while Copilot and Teams also experienced disruptions. Microsoft continues investigating and posting updates under incident references EX1550543 and MO1550821.