Microsoft outage sends businesses back to faxes and phones

For a stretch of hours this week, the most reliable communication tool in global finance was a fax machine.

A worldwide outage hit Microsoft’s Outlook, Teams and Copilot and left millions of people without email. Bankers, traders and shipping firms were among those caught out. Telephones, faxes and even Bluetooth file transfers filled the gap.

What broke, and for how long

The disruption to Microsoft 365 began around midday Eastern Time (17:00 GMT) on November 12. It reached users in at least 74 countries and territories.

It also lingered. The outage ran for roughly 12 to 18 hours. Microsoft reported signs of stabilisation by the afternoon of November 13, after rolling out fixes more broadly, as email delivery moved back toward normal levels.

Exchange Online, the backend that powers Outlook email, took the hardest hit. Mailboxes were delayed or could not be opened at all.

The damage spread past email. Teams, Copilot, SharePoint, OneDrive and Defender XDR all ran into connectivity problems or degraded performance.

Downdetector logged peak issue reports above 130,000 for Outlook alone. Microsoft has not given a total count of affected users. Microsoft 365 has an estimated user base of over 430 million globally.

Finance goes analog

Euronext, the European exchange operator, told listed companies to reach it by phone while it verified callers’ identities. That detail matters. When email fails, a phone call has to do double duty as both a channel and a security check.

Trading desks in Taiwan and Japan turned to faxes to confirm trades.

Most institutions reported that their core systems kept running. The outage hit the communication layer around those systems, not the systems themselves.

Airlines, health services and police forces were also affected. Some companies pushed back earnings releases or customer updates because they could not reliably get the word out.

Microsoft’s explanation

Microsoft traced the problem to a technical issue. Servers failed automated health checks while under elevated loads.

The company stressed that the outage was not caused by a cyberattack or by problems with AI.

The concentration problem

Many organisations run email, messaging, document storage, security tooling and now AI assistants through one provider. That setup is efficient and cheap to manage. It also means one bad afternoon at one company can ripple across airlines, hospitals, police forces and stock exchanges at once.

The firms that coped best were the ones with a fallback ready, whether that meant phone trees, fax lines or identity checks that work without email. Euronext’s phone verification process is a decent example of a backup that considers security, not just connectivity.