Microsoft links global Outlook outage to network upgrade

An outage that took down Outlook, Teams and Copilot in at least 74 countries was not a cyberattack, Microsoft says.

What happened

It started on Thursday afternoon, US time, as a problem with Outlook email and Teams in the Americas. Within hours it had spread around the world. Users in at least 74 countries reported problems, and Downdetector reports for Outlook peaked at more than 130,000.

It was not only email. TechCrunch reported that files and documents in the cloud, Microsoft's Copilot AI tools, the Defender security software and the Intune admin dashboards were all hit, and some users lost access to their cloud-based Windows PCs. In the UK on Friday morning, some councils and police forces warned that online services such as form submissions were affected, and the government said it was working with Microsoft.

Microsoft's early updates said many servers had become "unexpectedly unavailable", which pushed more load onto the rest and overwhelmed a core process. Engineers paused changes, restarted servers and brought them back in stages. Early on Friday, US time, Microsoft reported positive results from a fix, and it extended the time Outlook holds delayed email to 48 hours so messages would not be lost.

On Friday Microsoft gave its explanation. Failed automated health checks had taken servers out of service. The fault was introduced by an issue during an earlier network capacity upgrade and surfaced after a recent network change. Microsoft said it found no evidence of malicious activity, described it as a technical issue not related to cyber or AI agents, apologised, and promised a full post-incident report. Until that report is out, treat the explanation as preliminary. By Friday afternoon UK time, it said email queues were approaching normal levels.

Doug Madory of the network monitoring firm Kentik told TechCrunch the disruption lasted about 18 hours. Some reports put it closer to a full day, and some delayed email was expected to keep arriving after services recovered. This follows a days-long Microsoft outage in September, which the company blamed on a core authentication configuration issue.

Why it matters

Most mid-sized companies now run their email, documents, meetings, security and AI assistants through one supplier. That is efficient on a normal day. On a bad day it means one fault stops all of them at once.

The AI angle is quieter but real. As more work runs through Copilot and AI agents, an outage does not just stop people reading email. It stops the tools people now rely on to draft, summarise and act. The more AI you build on one platform, the more that platform's bad days cost you.

What it means for your business

This is not a reason to leave Microsoft 365. Every large cloud provider has outages, and moving is expensive and risky. It is a reason to know your plan B before you need it.

For a founder-led company of 50 to 500 people, the practical questions are simple. How do you reach your team and your top customers if email and Teams are down for a day? Where are the files you cannot work without? Who can approve a payment or sign a contract if the usual tools are offline? If your answer is "we would figure it out", you do not have a plan yet.

Also check your contract for a service level agreement and any credits after long outages. Ask your Microsoft partner or IT lead what applies to you, and read the post-incident report when it comes out. In the meantime, remind staff to ignore emails and texts posing as Outlook account-restoration messages, a phishing trick TechRadar flagged during the outage.

What to do this week

Set up one out-of-band way to reach your whole team and your top ten customers, such as a phone tree or a messaging group outside Microsoft. Run a one-hour tabletop exercise with your leadership team on "Microsoft 365 is down for 24 hours". Ask your IT lead or Microsoft partner what service credits you are owed and to share Microsoft's post-incident report.