On Thursday, November 12, 2026, email stopped working for millions of people around the world. Outlook would not open. Teams messages would not send. Copilot, SharePoint, and several other Microsoft services went down with them. The outage lasted more than a day, but on Saturday morning, November 14, Microsoft confirmed service was restored for the remaining customers and the delayed email had been delivered.
If your inbox went quiet on Thursday and Friday, this was why. Here is what happened, what Microsoft has said so far, and what you should check now.
What Went Down
The trouble started just after 1 p.m. Eastern time on Thursday, November 12. People trying to open their Outlook mailboxes got errors or endless loading screens. Within the hour, outage tracker Downdetector recorded more than 130,000 reports of problems with Outlook, and more than 46,000 reports for Microsoft 365 as a whole.
It was not just email. The outage hit Exchange Online, the service that powers Outlook mailboxes, and everything that depends on it went down too. Teams, SharePoint, Copilot, Microsoft Defender, Planner, To Do, Intune, Purview, and Power BI were all affected. Some people could not join meetings. Others could not open shared files or see their calendars.
Microsoft gave the incident two tracking numbers: EX1550543 for Exchange Online and MO1550821 for the wider Microsoft 365 services. The problems spread across the United States, Europe, Australia, and many other countries. Reuters reported that even Australia's spy agency and federal police were caught up in it, and the Australian government activated an agreement to get its services restored first.
How Big Was It?
Microsoft says more than 430 million people use its Microsoft 365 services. Not all of them were affected, but the outage reached governments, hospitals, schools, banks, shipping firms, and stock exchanges. European exchange operator Euronext told listed companies to use the telephone for urgent messages because its email was down. Some businesses went back to faxes, phones, and Bluetooth to get work done while email was out.
For many small businesses, the outage was a full working day lost. No email meant no orders confirmed, no invoices sent, and no replies to customers. Social media filled up with jokes about the "adult snow day," but for anyone whose business runs on Outlook, it was not funny.
What Caused It
Microsoft has been clear about two things: this was not a cyberattack, and it was not caused by artificial intelligence.
In a statement on Friday, November 13, Microsoft said the incident "was introduced by an issue during an earlier network capacity upgrade" that only surfaced after a recent network change. In plain English, a hidden bug from an earlier upgrade to Microsoft's network woke up when a new change was made, and it knocked servers offline.
Here is what happened next, in simple terms. A large number of Microsoft's servers unexpectedly became unavailable. The servers that were left had to carry far more traffic than usual. At the same time, many servers started failing their automated health checks, which are the routine tests that confirm a server is working properly. The process that sets up secure connections between services was overwhelmed, and that stopped people reaching their mailboxes.
Microsoft paused all changes to its systems, rerouted traffic, added extra capacity, and rolled back a recent network configuration change. By Friday afternoon it reported "broad recovery and stability across our services" and said the underlying issue had been addressed. On Saturday morning, Microsoft confirmed service was restored for the remaining customers and regions, and the delayed email backlog had been processed.
What Microsoft Has Not Said Yet
Microsoft has promised a full post-incident report once its review is complete, but as of Saturday, November 14, that report has not been published. Microsoft said a preliminary report will come within two working days and a final report within five. The company has not said how many customers were affected, or exactly what the bug was and why it stayed hidden for months.
That matters, because the same question will come up the next time a big cloud service goes down: how much of your business depends on one provider?
What to Do Now
If you use Outlook or Microsoft 365, here is a short checklist for the weekend.
1. Check your inbox and sent folder
Delayed email should arrive on its own. Microsoft extended the time it keeps trying to deliver delayed messages, so do not resend everything at once. Check your sent folder first. If a message shows as sent, the other side will probably still get it, just late.
2. Ask before you resend
If you sent something important on Thursday or Friday, a short message asking "did you get my email?" is better than sending the same email twice. Your customer or colleague may already have it.
3. Watch out for phishing
Big outages always attract scammers. Expect fake emails claiming to be from Microsoft, offering to "restore your account" or "fix your mailbox." Microsoft will not ask you to click a link to fix this. If you get one, delete it. This is a good moment to protect your online accounts with a strong, unique password and two-factor authentication, if you have not already.
4. Check your calendar and meetings
Teams meetings and calendar invites were affected too. If a meeting was booked or changed on Thursday or Friday, double-check it is still in your calendar before Monday morning.
5. Make a backup plan
This outage is a reminder that cloud computing is convenient, but it is still someone else's computer. If email is your business lifeline, have a second way to reach customers: a phone number on your website, a messaging app, or a second email address on a different provider. Write the plan down now, while the outage is fresh in your mind, so you are not working it out during the next one.
The Bigger Lesson
Microsoft 365 is one of the most widely used business tools in the world, and it was down for more than a day. The cause was not hackers and not AI. It was a bug in an upgrade, the kind of ordinary technical failure that can hit any large system.
For small businesses, the lesson is simple. You do not need to leave Microsoft 365, and you do not need to panic. But you do need a plan for the day it stops working, because this week showed that it can. Keep a backup way to contact your customers, keep your passwords safe, and check your inbox before you assume an email never arrived.
Microsoft says it will publish a full report on what went wrong. When it does, we will update this article with what it says.
