Microsoft Links Global Outage to Failed Health Checks

Microsoft linked a global Microsoft 365 outage to a problem causing servers to fail automated health checks and become unavailable, as disruptions to Outlook email and Copilot continued into Friday.

The company acknowledged Exchange Online mailbox access problems in the Americas at 12:54 p.m. ET Thursday, Nov. 12. Full service had not been restored by its 9:56 a.m. ET update Friday, more than 21 hours later. That notice still warned of intermittent connectivity issues and delayed email delivery.

Microsoft said it had “no evidence of malicious activity associated with this incident.” That was an assessment in its ongoing service-health notice, not a completed post-incident review: the company said a full report identifying the root cause would follow mitigation.

The company’s explanation so far describes lost capacity rather than a surge in demand. Microsoft said servers had unexpectedly become unavailable, straining the remaining infrastructure. It later identified an overwhelmed core process on affected servers that was causing capacity loss.

An alternative health-check method brought some servers back into service. But Microsoft later said recovered machines could become unresponsive again once they received traffic. Engineers were limiting traffic in some locations and rebuilding some servers using an earlier configuration to test whether that would keep them responsive.

Exchange Failures Reached Beyond Email

Microsoft’s service notice said the affected features depended on Exchange Online, its email service. Outlook users could lose mailbox access through web, desktop and mobile connections. Copilot users could be unable to load chats, receive responses or access work data such as email, calendars and files.

For developers, Microsoft Graph requests accessing Exchange mail, calendar and contact data could time out. Microsoft also listed intermittent problems with Intune device enrollment and compliance policies, and trouble loading some Microsoft 365 admin-center pages.

The disruption was not a blanket failure of every listed product. Most core Teams functions, including calls and chats, remained available, as did access to files stored directly in SharePoint Online, Microsoft said.

The consequences extended beyond office communications. The Supreme Court of the Philippines said its Philippine Judiciary 365 services, including Outlook, were affected and warned of delays to email responses and other transactions.

Ariel Healthcare, an NHS medical practice, warned that online consultations, patient messages, hospital correspondence and discharge information could be delayed. It asked patients not to submit repeat-prescription requests through its website forms, which use NHS mail, and to use the NHS app instead.

Microsoft extended its email timeout window to 48 hours to help protect delayed messages while it worked through mail queues and backlogs.