A critical Microsoft outage lasting more than 22 hours has raised questions about how heavily vital services rely on a handful of major tech firms.

The disruption, which affected Microsoft 365 services such as Outlook, was caused by routine automated checks that took some servers offline, overloading the remaining ones with traffic.

The recovery took nearly a full day while engineers gradually restored services, highlighting how embedded the tech giant’s services are in modern society.

Flora Hamilton, executive director of the Small Business Charter, said the outage was a “stark reminder” of how much firms “rely on digital systems” – like Microsoft Outlook – “to keep their operations running”.

“For many small and medium-sized enterprises (SMEs), access to email is fundamental to everything from communicating with customers and suppliers to generating income,” she said.

The disruption was not just confined to businesses, but also affected organisations and public institutions around the world.

Around 430 million people globally use Microsoft 365, and issues were reported across more than 70 countries.

The fallout from the outage had a wide-ranging effect, knocking out email systems for the US House of Representatives and Australian intelligence agencies, as well as disrupting court systems in Singapore and airline support desks in India.

Microsoft has since apologised for the issue, which it said was due to a technical failure rather than a cyber-attack.

There was no “ETA” for when services will be fully recovered, Microsoft added in a statement late on Friday (GMT).

Walter Pasquarelli, an AI strategist, told the BBC that for governments, businesses and critical infrastructure, the outage had “put their vulnerabilities and dependence in plain sight”.

“Looking ahead, as AI assistants are plugged into our email, calendars and files, a failure like this may spread even further,” he said.