Microsoft Outlook Down for 130,000 Users: What Caused the Outage
Outlook and Microsoft 365 went down for more than 130,000 users on Thursday as Microsoft traced the failure to its Exchange Online email system.
Image: Wikimedia Commons / Derrick Coetzee
Outlook and Microsoft 365 went down for tens of thousands of users across the United States on Thursday, after a failure in Microsoft's Exchange Online email system left people unable to open their inboxes. Microsoft confirmed the disruption on its Microsoft 365 Status account and said it was working to reduce the impact, tracking the incident as EX1550543.
Reports of problems began surging just after noon Eastern time, according to outage tracker Downdetector. Outlook reports climbed past 83,000 just before 1 p.m. Eastern and peaked at more than 130,000 by 1:27 p.m. Eastern, while reports for Microsoft 365 topped 46,000.
- More than 130,000 Outlook outage reports at the 1:27 p.m. Eastern peak; Microsoft 365 reports topped 46,000.
- Microsoft traced the failure to connectivity errors in part of the Exchange Online infrastructure that handles mailbox access requests.
- Outlook on the web, desktop and mobile apps were affected, along with Teams and Copilot.
- Microsoft paused deployments, shifted traffic and restarted servers; no restoration time had been given.
What Caused the Microsoft Outlook Outage?
Microsoft said it found connectivity errors affecting part of the Exchange Online infrastructure that receives and processes requests to open mailboxes. The company said it had collected networking logs to review, and it has not given a confirmed root cause. The notice listed Outlook on the web, Messaging API, Exchange ActiveSync and the REST API among the affected routes.
The failure spread beyond email. Microsoft said the issue could affect Microsoft 365 service connectivity for users in any region, after first describing the impact as concentrated in the Americas. Teams drew about 3,000 to 4,500 reports and Copilot, Microsoft's AI assistant, about 4,400 at the height of the disruption, days after Microsoft's researchers showed how a few neurons can hijack an AI agent.
How Many Users Were Affected by the Outlook Outage?
| Service | Peak outage reports | Time of peak |
|---|---|---|
| Outlook | More than 130,000 | 1:27 p.m. Eastern |
| Microsoft 365 | More than 47,000 | About 1:20 p.m. Eastern |
| Teams | About 4,500 | Afternoon |
| Copilot | About 4,400 | Afternoon |
By 1:50 p.m. Eastern, reports had begun to fall, with Outlook down to about 92,900 and Microsoft 365 to about 37,000, but Microsoft said the problem was still being fixed as of 2:40 p.m. Eastern. The company warned that moving traffic to other infrastructure could cause delays for some users. OpenAI said it was investigating a problem with Microsoft connectors.
When Will Outlook Be Back Online?
Microsoft has not given a confirmed time for full restoration. The company said it had paused all deployments and configuration changes, was moving traffic off the affected infrastructure and was restarting servers to return them to service. Administrators can follow the incident in the Microsoft 365 admin center under EX1550543.
The outage came two days after Microsoft warned about an actively exploited Outlook security flaw. An earlier Teams disruption in North America was fixed before the email outage peaked. It hit one of the world's largest software companies days after Microsoft overtook Nvidia as the second most valuable listed company.
Frequently Asked Questions
Is Outlook down right now?
Outlook and Microsoft 365 suffered a widespread outage on Thursday, November 12, with reports peaking above 130,000 in the early afternoon Eastern time. Microsoft had not confirmed full restoration; users who cannot open mailboxes should check incident EX1550543 in the Microsoft 365 admin center.
What caused the Microsoft 365 outage today?
Microsoft said connectivity errors affected part of the Exchange Online infrastructure that receives and processes mailbox access requests. The company is reviewing networking logs and has not announced a confirmed root cause.
Which Microsoft services were affected by the outage?
Outlook was hit hardest, through Exchange Online, along with Microsoft 365, Teams and Copilot. The failure could hit every route into a mailbox, including Outlook on the web, desktop and mobile apps, and the MAPI, Exchange ActiveSync and REST connections.
How do I know if my Outlook email is affected?
If Outlook will not load, sign-in fails, or sent mail is delayed, the mailbox may be caught in the outage. Administrators can track incident EX1550543 in the Microsoft 365 admin center.
Microsoft is expected to post further status updates during the afternoon, and it has not said when it will publish a full account of what caused the failure.
