The Microsoft Outlook outage stretched past eight hours Thursday night, leaving users across North America and beyond without reliable email as Microsoft struggled to keep its own servers running.
The trouble started just before 1 p.m. ET on Thursday, November 12. At 12:54 p.m. ET, Microsoft said it was investigating problems with users reaching their Exchange Online mailboxes in the Americas. Exchange Online is the system that powers Outlook email for businesses, schools and organizations, so when it struggles, inboxes stop loading, messages stop sending and new mail stops coming in. Minutes later, Microsoft warned that the problem could affect Microsoft 365 connections for users in any region.
Downdetector, the website that tracks user complaints about service problems, logged more than 130,000 reports of Outlook issues at the peak shortly after 1 p.m. ET. Reports eased through the afternoon but were still above 30,000 into the night. Those numbers reflect complaints submitted by users, not a confirmed count of affected customers.
Outlook was not the only casualty. Teams, SharePoint Online and Microsoft 365 Copilot were all caught up in the disruption, and by late afternoon Microsoft had added Intune, Defender for Office 365, Purview and Power BI to its list of affected services.
Microsoft said the problem started when a number of its servers became unexpectedly unavailable. That forced the servers still running to carry extra weight across multiple regions, which led to the connection failures. The company stressed that the pressure did not come from a surge in users. Instead, servers were failing automated health checks, the routine tests that decide whether a server is fit to handle traffic, and dropping out of service.
To stop the bleeding, Microsoft paused all deployments, shifted traffic away from the struggling infrastructure and began restarting affected servers. Around 3:19 p.m. ET, the company said it had not found any recent change that lined up with when the Microsoft Outlook outage began.
The fixes did not hold. Around 6 p.m. ET, Microsoft said it had returned a portion of the affected servers to service and that they were stable. It later updated that those same servers can become unresponsive again once traffic reaches them. Microsoft acknowledged that the actions it had taken so far had not provided the relief it expected, explaining that a core process on the affected servers was getting overwhelmed and causing them to lose capacity.
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Engineers are now preparing an automated recovery process that constantly detects servers that stop responding and restarts them so they stay in service while a broader fix rolls out. Microsoft also said its review of recent changes turned up a small number of configuration updates it is investigating as possible contributors, a shift from its earlier statement that no recent change matched the start of the outage. The company has not confirmed a root cause, and nothing released so far ties the outage to a cyberattack.
The fallout reached far beyond office inboxes. In Canada, a Toronto hospital network declared a Code Grey, the alert hospitals use when critical infrastructure fails. VIA Rail reported problems, and the University of Toronto, Seneca Polytechnic and George Brown Polytechnic said their email services were affected. The outage also disrupted Microsoft connections used by AI companies OpenAI and Anthropic.
As people scrambled for backup options, Downdetector showed rising complaints about Gmail, Zoom and Yahoo Mail. Gmail problems were flagged starting at 1:05 p.m. ET, with more than 1,000 reports by 5:15 p.m. ET. Google has not confirmed an outage.
As of 9 p.m. ET, Microsoft said repairs were underway but had not given a timeline for full recovery. The company says users should expect service to return gradually as Outlook and its other apps reconnect. Business administrators can follow the Microsoft Outlook outage in the Microsoft 365 admin center under incidents EX1550543 and MO1550821.
