Microsoft 365, the company's cloud subscription, includes Outlook, Teams and the Copilot artificial intelligence assistant. All three were affected by connectivity problems, the BBC reported. More than 430 million people use Microsoft 365 apps, according to Microsoft's website.
The company said on Friday it had not found malicious activity causing the disruption and blamed elevated infrastructure loads. On Thursday it said efforts to repair Outlook were not going as expected and that it was seeking alternative solutions.
Access varied. Many customers could not send or receive email, view certain files or open details in calendar apps. Some users could still use Teams for messaging and online meetings.
Microsoft said a large number of servers became"unexpectedly unavailable", sending added traffic onto the servers that remained online and straining them.
In posts on X, Microsoft said changes meant to improve service were not working as planned."We've monitored the status of the changes applied to improve serviceability and confirmed they're not taking as expected,"the company said. It added that it was"identifying alternate workstreams that can be applied to increase capacity"and did not say when full service would return.
As the outage dragged on, Microsoft posted further updates describing continued but unsuccessful efforts to restore service. It later said it was seeing improvements in stability and capacity after its latest traffic optimisation measures, and said it would"continue to treat this incident with urgency and priority until full resolution".
The impact was felt by companies and governments that rely on Outlook to communicate. Microsoft 365 is used by organisations worldwide, and the outage was expected to have a knock-on effect on other services.
GP surgeries, pharmacies and schools across the UK were also affected. Government agencies elsewhere reported problems, including the Singaporean government and Australia's spy agency.
Reports of the outage said it also affected all New Zealand embassies, consulates and representative offices around the world.
European stock-market operator Euronext advised listed companies to use the telephone to communicate corporate information because of the Microsoft outage.
Tech companies that depend on Microsoft's infrastructure were hit as well. OpenAI and Anthropic both reported problems. ChatGPT maker OpenAI said it was investigating an issue affecting its connections to Microsoft's services that had caused some tools not to work as expected.
Microsoft has said the outage was not caused by a cyber-security incident. France 24 reported that the company was"not aware of any malicious activity"behind the Outlook disruption and blamed elevated infrastructure load. It has not given a time for full restoration.