If your Outlook inbox refused to load on Thursday, you were not alone. A widespread Microsoft 365 outage on November 12 left users around the world without email, disrupted Teams features and caused trouble for AI tools that connect to Microsoft’s services. Here is a plain-English look at what happened, why so many tools were affected and what is still unclear.
This post is based on reporting from Open Magazine, and the situation may have changed since publication.
What Happened During the Microsoft 365 Outage?
The disruption began during the US workday on Thursday, November 12, and carried into Friday morning in India. According to the report, some users could not open their Outlook inboxes, emails were delayed, and features in Teams and Microsoft’s AI assistant, Copilot, stopped working properly.
Downdetector logged about 138,000 Outlook problem reports at the US peak. For some users, the disruption lasted more than five hours. These figures are user-submitted reports, so they show how many people flagged a problem and not the exact number of affected accounts.
Is Outlook Working Again?
Recovery was partial at the time of the report. By early Friday in India, Microsoft had restored some capacity, but full recovery was not confirmed. Some servers worked after a restart and then stopped responding once they started handling requests again.
Microsoft was testing a fix on a small group of machines and had begun rolling back a recent change to its network settings. Some customers could reconnect while others still had trouble reaching their mail.
Which Part of Microsoft 365 Broke?
The main problem was with Exchange Online, the service that stores and delivers work email and runs calendars for Microsoft 365 customers. Outlook is the app people use to reach that service. When Exchange Online can’t respond, the app may open but the inbox will not load, or messages will arrive late.
Microsoft logged mailbox trouble from about 9:47 p.m. IST on Thursday. It recorded the wider Microsoft 365 incident separately from about 11:56 p.m. IST.
What Caused the Outage?
Microsoft said software that sets up secure connections on the affected servers became overwhelmed. As servers dropped out, fewer machines remained to handle incoming requests, which put more strain on the rest.
The company was also checking whether a network settings change made around the start of the incident played a part. A Microsoft spokesperson told The Guardian that there was no sign of a cyberattack. The root cause had not been fully confirmed.
Why Teams Calls Worked but Calendars Failed
Some people noticed that they could join a Teams call but could not schedule one. According to Microsoft, Teams chat and online meetings stayed largely usable. Scheduling a meeting or opening a calendar depends on Exchange Online, which is why those features failed. Teams had also had a separate messaging problem earlier on Thursday, which was fixed.
Why Did ChatGPT and Claude Have Problems?
AI assistants can connect to your work email, calendar and files through Microsoft 365 connectors, with your permission. When Microsoft 365 had trouble, those connectors failed.
OpenAI said new connections and some functions might not work. Anthropic said most requests involving mail, calendar and search through its Microsoft 365 connector were failing, and it also flagged problems with Claude inside Outlook. Microsoft’s own Copilot struggled to access work email, calendars and files. The outage shows how closely AI tools now depend on the same cloud services as everyday office software.
How Far Did the Outage Spread?
Microsoft first identified mailbox problems in the Americas and later said users in any region could be affected. In Australia, Service NSW asked customers to delay visits to its centres because some transactions were unavailable. In the US, electric-truck maker Workhorse postponed its earnings call by four days because of the disruption.
There was no reliable India-specific count of affected users or organisations at the time of reporting.
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Has This Happened Before?
Yes. Outlook and Teams both had trouble on January 25, 2023, when a change to Microsoft’s global network interfered with connections to Microsoft 365 and Azure. In October 2025, a failure in Azure Front Door, a service that directs internet requests to the right servers, also disrupted Microsoft 365.
The pattern is similar each time. Users see problems in the apps they open, but the failure starts in the systems behind them.
What Should IT Teams and Users Do Now?
- Check the Microsoft 365 admin centre. Administrators can follow the wider incident under MO1550821 and the mailbox incident under EX1550543.
- Test your email and calendar. Once Outlook opens again, confirm that new messages arrive and calendar invitations go through.
- Have a backup plan. Keep a second way to reach your team, such as a phone number or another messaging app, for critical meetings.
- Expect delays. Emails sent during the outage may arrive late, so follow up on anything urgent.
The Bottom Line
This Microsoft 365 outage is a reminder of how much of modern work runs on a few shared cloud providers. A problem in one email service disrupted inboxes, calendars, Teams scheduling and several AI assistants at once. The real test for Microsoft is whether the repaired servers keep working as normal traffic returns, and whether its final explanation identifies what set off the failure.
