What we know as of Friday, November 13, 2026, 10 AM Eastern. We'll update this page when Microsoft publishes the root cause.
The short answer
On Thursday, November 12, starting around 12:30 PM Eastern, Microsoft 365 email began failing for businesses worldwide. Microsoft says servers in Exchange Online, the one service that holds every mailbox, started failing their own automated health checks. The servers left standing took on their load and were overwhelmed too, and servers brought back online were knocked over again by the traffic waiting for them. Microsoft says it has no evidence of an attack.
What stopped working, and what didn't
The pattern is the clue. Everything that broke needed your mailbox.
- Stopped: sending and receiving email, calendar invites, Copilot, Planner, and printing through Universal Print.
- Kept working: Teams calls, meetings and chats, and files stored directly in SharePoint.
Within about an hour, Downdetector was showing problems in 74 countries, with about 130,000 Outlook reports shortly after 1 PM Eastern (Downdetector, reported by AP and Reuters).
Why did email go down?
Here is what Microsoft has said in its status updates, in order:
- Servers began failing their own automated health checks and became unavailable.
- The load moved onto the remaining servers. Microsoft said this was not an overall rise in traffic, but a large number of servers being unexpectedly unavailable.
- A process on the affected servers that sets up secure connections became overwhelmed.
- Servers that came back could become unresponsive again as soon as traffic reached them.
Microsoft has not yet said what started the first failures. It has promised a full post incident report once the problem is fixed.
Was it a cyberattack?
Microsoft said it has no evidence of malicious activity associated with this incident.
Was it caused by an update?
Not confirmed. Microsoft said it reversed a recent network configuration change that lined up with the start of the problem, but it has not called that change the cause. Australia's Minister for Home Affairs and Cyber Security, Tony Burke, described it as "an update that has gone awry". Microsoft has not confirmed that.
Is it fixed?
Mostly. On Friday morning Microsoft said email queues were significantly reduced and approaching normal levels, but it still listed the incident as a service degradation. Microsoft's incident numbers are EX1550543 and MO1550821, for anyone checking their own admin center.
What to do the next time email goes down
- Check Microsoft's status page, status.cloud.microsoft, before changing anything on your own computers.
- Move urgent conversations to the phone, or to Teams if Teams is working.
- Don't keep resending the same message. Mail held up during an outage is delivered as service recovers.
- Afterward, write down who calls whom the next time email is down, including your customers and your IT provider.
What we do for our clients
When Microsoft has a bad day, we watch the incident, tell our clients what's affected and what isn't, and keep the phone line open. Clients can always reach us at 800-683-7552, or through the Electric Software agent on their computer, even when email is down.
Sources
- Microsoft 365 status updates and admin center notices, November 12 and 13, 2026, as quoted by The Register, XDA and CNBC.
- Downdetector figures and the minister's comment, reported by AP and Reuters via Al Jazeera on November 12 and November 13.
- Start time from network monitoring by ThousandEyes.
- Incident numbers from SecurityWeek.
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