Microsoft Outage Hit 140,000 Outlook Users Across 74 Countries

Nearly 140,000 people in 74 countries reported Outlook failures at the peak of a global Microsoft outage on Thursday, according to monitoring website Downdetector. Microsoft has ruled out a cyber-attack. Its engineers have, by the company's own admission, achieved only "marginal success" in restoring service.

The disruption hit Microsoft 365 services including Teams, Outlook and the AI assistant Copilot, which Microsoft attributed to "connectivity problems." Many customers could not send or receive email, open certain files or see calendar entries. Some Teams users noticed nothing at all and continued messaging and joining online meetings as normal — a patchiness that makes the true damage harder to measure.

How far does the damage reach?

Microsoft says more than 430 million people use Microsoft 365 apps. That is the denominator that matters: Downdetector's 140,000 reports represent only those users who both noticed a failure and filed a report, so the affected population is almost certainly far larger.

The blast radius extends well beyond Microsoft's own products. OpenAI, the maker of ChatGPT, said it was investigating an issue affecting its connections to Microsoft services, which caused some tools not to work as expected. Rival AI firm Anthropic also reported problems stemming from the outage — an unusual case of two competitors knocked sideways by the same infrastructure failure.

Government operations felt it too. The Singaporean government and Australia's spy agency both said the outage affected them. In the UK, several GP practices warned of potential disruption, with some instructing patients to raise urgent queries by phone rather than by email or web form.

The lesson for corporate risk officers: a single vendor's capacity problem can cascade into healthcare, government and competing AI platforms within hours.

What actually went wrong?

Microsoft has attributed the outage to "elevated load" on its infrastructure — industry shorthand for servers handling far more stress than usual. A large number of servers became "unexpectedly unavailable," the company said, pushing their traffic onto the remaining servers and straining those in turn. That is a cascading failure, not an external attack.

The fix has not gone smoothly. In an earlier statement, Microsoft conceded that its attempted remedies were "not taking as expected." In its latest update, the company said it had observed "marginal success" and was continuing to monitor activity across regions, evaluate server status and determine what actions could improve capacity.

Note what Microsoft has not said: no timeline for full restoration, no explanation of why the servers became unavailable in the first place, and no confirmed figure for how many users were affected. "Marginal success" two days into a global incident is a modest promise, and the company has offered little to back it.

What do experts say the cost is?

Australian cyber-security expert Troy Hunt told the BBC the outage could have far-reaching consequences. "Microsoft is a massive part of the internet backbone and reminds us how critical email still is," Hunt said. "Not only does this outage affect many people's ability to work but also things like the ability to communicate about appointments, purchase things that need verification, create or access accounts and services."

Paul Spain of New Zealand-based advisory firm Gorilla Technology put a blunter price on it. With email and services offline, he said, companies have practically "lost a business day," which is frustrating users. For a mid-sized firm, one lost working day can mean thousands of hours of unproductive payroll — a cost no vendor statement will quantify.

In plain terms: the world's largest software vendor could not keep its own email running, and no one has yet explained why. Until Microsoft publishes a root cause, every business running on Microsoft 365 is carrying a risk it cannot price.

By Olivia Hart for Business Bearings