Microsoft’s Outlook email service and other Microsoft 365 tools went down for hours on Thursday, 12 November 2026, leaving workers across the United States unable to reach their inboxes, calendars and Teams chats. Downdetector recorded more than 130,000 reports of Outlook problems around 1:27 p.m. ET, according to Reuters, while Microsoft said servers had unexpectedly become unavailable.
The disruption struck in the middle of the workday and spread well beyond email. Teams, the Copilot AI assistant, SharePoint and other Microsoft 365 services were also affected, and Microsoft warned that users in regions outside the Americas could be hit as well.
How the outage unfolded
Microsoft first said it was investigating problems reaching Exchange Online mailboxes at 12:54 p.m. ET, after reports of trouble began climbing shortly before 1 p.m. ET. An earlier, separate Teams disruption in North America that morning had already been fixed around noon.
| Service | Downdetector reports at peak |
|---|---|
| Outlook | More than 130,000 |
| Microsoft 365 | More than 46,000 |
| Copilot | About 4,400 |
| Teams | About 3,000 |
Downdetector counts user-submitted reports, so the figures show the scale of the complaints rather than a verified count of affected customers. Even so, the spike was steep: Outlook reports climbed from tens of thousands to six figures within the hour.
Servers failed their health checks
Microsoft first blamed elevated load across its infrastructure, then said a number of servers had unexpectedly become unavailable, straining the rest. The company said some servers were failing automated health checks, the pulse tests that decide whether a server receives traffic, according to CNBC.
Engineers restarted servers and moved traffic to other routes, but Microsoft warned that restored servers could become unresponsive again once traffic returned. By Thursday evening the company said its actions so far had not brought the relief it expected.
Microsoft also said it was not aware of any malicious activity behind the incident, according to CNBC. It has not yet published a final root cause, and said it would release a full report once the problem was fixed.
Service returns, slowly
By early Friday morning, Microsoft said it had restored access to the affected services and that mail flow remained stable. Reports on Downdetector had fallen sharply from the afternoon peak, though more than 18,000 people were still reporting Outlook problems late on Thursday night.
Microsoft is tracking the mailbox disruption under incident reference EX1550543 and the wider Microsoft 365 outage under MO1550821. Administrators can follow both references on the company’s service health dashboard.
Copilot’s outage lands in a bruising week for AI
The timing stung because Copilot, Microsoft’s AI assistant, was among the services knocked out. The outage came in a week when the wider AI sector was already under pressure, even as Anthropic’s blockbuster IPO valued the Claude maker at up to $1.4 trillion, and Nvidia’s boardroom turmoil sent the chipmaker’s shares sliding.
What to check if your inbox still is not working
If Outlook is still failing, first check the live status on Downdetector’s Microsoft 365 page to see whether reports are still elevated in your area. Then try the Outlook web app if the desktop app fails, or the reverse, since the two connect through different routes and one may work while the other does not.
Business users should also ask their IT administrator to check the Microsoft 365 admin centre, where the incident is listed under references EX1550543 and MO1550821. Unsent mail should queue and send once the connection is restored, so there is no need to resend messages repeatedly.
Microsoft 365 outage: questions answered
When did the Microsoft 365 outage start?
Reports began climbing shortly before 1 p.m. ET on Thursday, 12 November 2026, and Microsoft said it was investigating Exchange Online mailbox problems at 12:54 p.m. ET.
What caused the Microsoft 365 outage?
Microsoft said a number of servers unexpectedly became unavailable and were failing automated health checks, straining the remaining infrastructure. A final root cause has not yet been published.
Was the outage a cyberattack?
Microsoft said it was not aware of any malicious activity behind the incident, according to CNBC.
Is Microsoft 365 back now?
Microsoft said early on Friday, 13 November, that it had restored access to the affected services and mail flow remained stable, though it continued monitoring the restored servers.
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