What happened
From Thursday evening, 12 November 2026, into Friday, Microsoft 365 was disrupted worldwide. Email (Outlook and Exchange Online) and calendars were hit hardest, followed by Teams, SharePoint, Copilot and other services that depend on Exchange Online. Microsoft tracks the incident in the admin centre under EX1550543 and MO1550821 (Born’s IT blog, SecurityWeek).
In broad strokes:
- Thursday evening: First failures in Outlook and Exchange Online, spreading to many countries within a short time. Mailboxes could not be opened in the browser, in Outlook or on mobile, and emails arrived late or not at all.
- Overnight: Microsoft restarted affected servers and rolled back a configuration change. Some of the restarted servers failed again under load.
- Friday: Services were gradually restored, traffic was slowly ramped up and the backlog of emails was worked through.
According to the latest information, services are running stably again; brief delays may still occur occasionally. You can always check the official status at status.cloud.microsoft.
The cause
According to Microsoft’s information so far, an internal check that continuously monitors whether servers are “healthy” failed under high load. Affected servers were therefore treated as faulty, the remaining ones had to take on more load – and the problem spread across several regions (IT-Administrator).
There is no indication of a cyberattack. Microsoft usually publishes a final root-cause report only after a full review.
What this means for you now
- Emails are generally not lost. Messages that could not be delivered during the outage are automatically resent by the sender’s server. They arrive late – in some cases hours late.
- Please don’t resend. Otherwise messages arrive twice. Notices such as “delivery delayed” are normal these days.
- Check important messages. If you are expecting a medical report, a deadline, an order or an invoice and the email still hasn’t arrived, ask the sender. Where deadlines are involved, a quick phone call is better than waiting for an email.
Beware of phishing
Large outages are usually followed by fake emails about “account repair”, “unlocking your mailbox” or “resetting your password”. Don’t click such links and don’t enter any login details. How to spot phishing and train your team is covered on our IT security page.
Our assessment
Microsoft 365 is a reliable service – but no provider is immune to outages. Cloud, your own server or a data centre: almost every IT environment today depends on services you don’t control yourself. Running your own mail server would not simply have “prevented” this outage either; it comes with risks of its own.
So the key question is not whether an outage will happen, but how well you can keep working when it does:
- Can you keep looking after your patients, clients or customers when email and calendars are down?
- Do your staff know what to do – and whom to call?
- Is it clear what needs to be up and running first?
These are exactly the questions we answer with our clients in the free security check.
These are exactly the points where an outage like this is felt in day-to-day work: appointments can’t be viewed in the calendar, reports and documents arrive late, and the question “Is it us or Microsoft?” costs time.
How to prepare for the next outage
A few measures help straight away – whether you use Microsoft 365 or another solution:
- Define critical processes: What must always work – such as practice software, e-card, telephony, appointment scheduling, files or the deadline calendar? And what can wait a day?
- Set recovery times: For each area, decide whether hours or a day are acceptable – and how up to date your data needs to be in an emergency.
- Stay reachable: A phone system, call forwarding and an emergency announcement ensure that patients, clients, customers and suppliers can reach you even without email. A phone system that doesn’t run through Microsoft Teams stays reachable during a Microsoft outage.
- Back up your data – in the cloud, too: Microsoft 365 protects against infrastructure failure, but it does not replace your own backup of mailboxes and files.
- Write down an emergency plan: Who decides, who informs whom, what is restored in which order? A one-page plan helps more in an emergency than anyone’s memory.
- Receive status notifications reliably: If Microsoft’s service notifications go to an Exchange Online address, they won’t arrive precisely when Exchange is down (Der Windows Papst). A second address outside Microsoft 365 or SMS notifications solve this.
The free security check for our clients
If you are an IT United client and an expected email is still missing, please contact support – we’ll check the delivery for you.
So that you are prepared for the next outage, we offer our existing clients the joint security check – free of charge. In a joint session, we go through your IT step by step and agree:
- what must always work – such as practice or law firm software, e-card, telephony, appointments, files or the deadline calendar,
- how quickly it needs to be back – hours or a day, you decide for each area,
- how up to date your data needs to be in an emergency – and whether your backup already delivers that today,
- how you stay reachable – for patients, clients, customers and suppliers,
- where your security has gaps – from access rights and updates to phishing protection.
You receive a written agreement on what will be restored in which order in an emergency, and a prioritised list of next steps.
→ Book your free security check now – or simply ask your contact at IT United. All the details are on our IT security page.
Not an IT United client yet? We’re happy to look at how well your organisation is prepared for the next outage in a free initial consultation. Find out more about our work with cloud and Microsoft 365 on the service page.
