Microsoft 365: Outlook goes down in 74 countries, cause still unknown

On Thursday 12 November 2026, Outlook called in sick without telling anyone. Exchange Online, the email service behind Microsoft 365, stopped responding for a large number of users, who could no longer open their mailbox or send or receive email. Le Monde Informatique reports, in an article published this Friday 13 November in the morning, that Microsoft had still not confirmed a lasting recovery nearly 11 hours after the first disruptions.

74 countries and a counter going haywire

According to Downdetector, quoted by the outlet, problems were reported in 74 countries and territories. In the United States, more than 130,000 reports about Outlook were logged at the peak of the outage. That figure is based on what users chose to declare and is not the number of people affected. What it mostly measures is how many people, deprived of email, went to check that it wasn’t just their Wi-Fi.

The damage was not limited to individual inboxes. The US House of Representatives ran into IT difficulties, and several Australian government agencies reported disruptions to their communications. The American company Workhorse Group pushed the presentation of its third-quarter results, scheduled for the 12th, back to 16 November, citing the outage.

One saturated process, then the dominoes

Microsoft first pointed to an overload of some components of its infrastructure. Its investigation then named a more specific culprit: a process responsible for establishing secure connections on the affected servers was saturated, which prevented those servers from handling requests normally.

You know how the rest goes. The unavailable servers sent their traffic to the ones still standing, which started to struggle in turn. The teams redistributed connections, restarted machines and restored some configurations. Several servers nevertheless fell over again after being brought back into service. It’s “have you tried turning it off and on again” at planetary scale, with the result every help desk knows by heart: it works, and then it doesn’t.

The trigger itself had not been identified at the time Le Monde Informatique was writing. Charles Lamanna, a Microsoft executive, said nothing suggested malicious activity or a cyberattack. The investigation into the exact cause was continuing.

Teams still standing, minus the calendar

Teams came through better than email. Chat and video calls broadly kept working. Calendars and meeting scheduling, which depend on Exchange Online, dropped out instead. So you could still hold your meeting, provided you remembered it existed.

Features in Copilot, SharePoint Online, Planner and some admin tools were also affected. And the outage spilled beyond Microsoft’s own walls: OpenAI and Anthropic reported problems with their Microsoft 365 connectors, which disrupted access to email and calendars from their assistants. An AI that can’t read your email is in exactly the same boat as you, only without the swearing.

What the outage says about your dependencies

For CIOs, the episode throws a harsh light on how concentrated business applications are with a single vendor. When Exchange Online goes down, internal communications, business processes and the third-party services plugged into its interfaces go down with it. Few architecture diagrams show that dependency as clearly as a day without email.

So this is a good moment to reread your business continuity plan. Start by checking it isn’t stored in SharePoint.