It started unspectacularly: Outlook could not connect to the mailbox. Anyone who assumed their own network was at fault restarted Outlook, then the computer, then the router. Two hours later it was clear the router was not the problem: Microsoft had a global outage hitting Exchange Online, Teams, SharePoint Online, Copilot and a long tail of other services — and it was still not fully over on Friday morning.
What happened on 12 November 2026
Microsoft published two incidents in the admin center. EX1550543 covers Exchange Online, the mailbox behind Outlook, starting at 11:17 a.m. Eastern — 17:17 CET. MO1550821 followed at 1:26 p.m. Eastern and lists the services dragged in with it: Teams, SharePoint Online, Microsoft 365 Copilot, Defender XDR, plus Planner, To Do, Intune, Purview, parts of Power BI, Universal Print and, in some setups, Windows 365 Cloud PCs.
Important for scale: what was affected were the parts that depend on Exchange Online. In Teams, chat and running meetings kept working, but calendars and scheduling did not. Files in SharePoint still opened. It was not a total product failure, it was a failure of the shared middle — and in Microsoft 365 that middle hangs off one identity, one tenant and one mail service.
The timeline, as far as Microsoft published it
| Time (CET) | What Microsoft reported |
|---|---|
| 17:20 | Investigating a possible problem with Exchange Online. |
| 18:45 | Connection errors in the part of Exchange Online that accepts logins and mailbox requests. |
| 19:27 | Infrastructure under heavy load in several regions; restarts and traffic shifting begin. |
| 20:30 | The load is not coming from more requests: a large number of servers dropped out of service unexpectedly. Microsoft pauses its own deployments. |
| 20:58 | The servers fail automatic health checks — the fault may sit in the part that answers those checks. |
| 23:03 | The actions so far "have not provided the anticipated relief". |
| 01:12 | The overwhelmed process is the one that sets up secure connections (TLS). Microsoft starts rolling back a recent network configuration change. |
| 02:48 | Restarts show "positive results", first regions recover. |
As of Friday morning there was no confirmed root cause, only a preliminary technical explanation. Microsoft stated repeatedly that it saw no indication of malicious activity. More than 130,000 reports piled up on Downdetector alone.
What the outage teaches technically
Three things stand out, and none of them is a Microsoft problem in the narrow sense.
First: the trigger was not an attack and not data loss, but a health check that removes servers from service. That is exactly the intended behaviour — it just caught too many servers at once, at the wrong moment. Automation without a manual escape hatch scales mistakes.
Second: a single overwhelmed process for secure connections was enough to make mailboxes unreachable. If you think of mail as "just storage", you underestimate the chain: DNS, TLS, auth, mailbox, client. Any link can stop the whole thing.
Third: the 99.9 percent availability in the SLA sounds like "almost always". A 30-day month has 43,200 minutes, 0.1 percent of that is 43 minutes. An outage of this length blows the monthly target for many customers. The remedy is a credit on the monthly bill — not automatic, on request, and it does not replace a lost workday.
The real dependency is identity
What actually failed during those twelve hours was not Outlook. It was the anchor everything else hangs from: if you cannot sign in, you cannot open files, see appointments, schedule a meeting, approve something and — with Teams Phone — you cannot even make a call. A mailbox today is rarely just a mailbox. It is the login, the calendar, the chat, the archive and often the second factor for authentication.
This is not a criticism of cloud, it is a description of the architecture. Putting office communication into one tenant buys convenience, versioning and operations — and pays with a shared failure point. That is a deliberate trade-off, as long as it is made deliberately.
What Nextcloud replaces — and what it does not
After a day like this the question is inevitable: "why not self-host everything?" The honest answer is more nuanced than either camp likes.
| Building block | Nextcloud | Note |
|---|---|---|
| Files & sync | yes, with versions and trash | The desktop client keeps selected folders available offline. |
| Calendar & contacts | yes (CalDAV/CardDAV) | Works in Thunderbird, Apple Calendar, Android and iOS without the web login. |
| Chat & video calls | yes (Talk) | A good base for internal calls; it does not replace Teams telephony. |
| Editing documents | via Collabora/OnlyOffice | Solid for most documents, not feature-parity with Word. |
| Mailbox | no | Nextcloud is not a mail server. A mailbox needs its own MX or another provider. |
| Phone system | no | Anyone using Teams Phone needs a separate solution. |
So Nextcloud covers a large part of the office day — files, calendar, contacts, chat, documents — but it is not an Exchange replacement and not a phone system. Claiming otherwise builds the next disappointment. Separating it cleanly wins exactly what this is about: a piece of infrastructure you can see yourself.
"Everything under control" does not mean "it never breaks"
Self-hosting is not automatically more reliable. A single server is a single point of failure, a forgotten update is a security risk, and a backup with an untested restore is data loss on a delay. The difference is not the probability of failure, it is the ability to act:
- Logs: you can see which process did what and when, instead of waiting for a status message.
- Update timing: you decide when to update — and you can plan a rollback instead of suffering one.
- Data: files and calendars live where you can back them up and restore them.
- Communication: you can explain what is going on, because you can trace the cause yourself.
Control is not a guarantee, it is the ability to act when it matters. Which is exactly what most Microsoft customers could not do on Thursday: they could wait and refresh the status page.
What I would check in one hour
Whether you run Microsoft 365, Nextcloud or both, these seven points are cheap and pay off during the next outage:
- A contact list outside the system: key customers, vendors, mobile numbers. Printed, or in a notes tool that does not hang off the same login.
- A second communication path: a Signal group, a phone chain or a chat outside the tenant — decided in advance and circulated, not on the day of the outage.
- Files available offline: keep the five documents a workday cannot run without on the device (Nextcloud client or "always keep on this device").
- One person who says "it's Microsoft": check the status page instead of reinstalling Outlook. Publicly reachable: status.cloud.microsoft.
- Check scheduled jobs: scan-to-mail, Universal Print, automatic invoices, forms, voicemail-to-mail. These fail quietly and surface only when a customer asks.
- Test restores, don't just own backups: restore one file and one mailbox per quarter — with a stopwatch.
- Check your own reachability: MX, SPF, DMARC and the externally visible endpoints. The mail DNS check and the Nextcloud check run without a login and show what the outside world sees.
And Thursday's mail?
Usually delayed, not lost. A sending mail server must retry for at least four to five days before giving up, per RFC 5321. If you are waiting for a signed contract or a bid, call instead of waiting. And if you wrote messages during the outage: check the outbox, do not blindly resend.
Then comes the unpleasant part that follows every large outage: phishing with the story "your mailbox has been restored, please sign in again". No provider asks for a fresh login via an email link during or after an outage. The scam radar collects exactly these patterns.
Bottom line
Thursday's outage was not proof that cloud does not work. It was proof of how much now hangs off a single identity — and how little any one company can do when that identity disappears. If you know the dependency, you can shape it: a clear view of what is truly critical, a second path for communication, and a remainder you control yourself.
For me that means: files, calendars and contacts in my own Nextcloud, with the versions and their end-of-support dates in sight — and something I can check from the outside. Everything under control is not a state, it is a practice.
The dates when the versions in use leave support are in the end-of-life calendar, including a subscribable calendar file. The next outage is coming; the only question is whether it catches you by surprise.