Microsoft 365 Outage Is Different: Email Queues Slow the Fix
Microsoft's 365 outage, which began Thursday, November 12, 2026, hit email, Teams and Copilot in at least 74 countries. Email's store-and-forward design means a backlog of retried messages slows recovery long after the fault is fixed, experts said.
The Microsoft 365 outage that began on Thursday, November 12, 2026, took down Outlook, Teams and the Copilot AI assistant for close to 24 hours and affected users in at least 74 countries. It is different from most cloud failures because email keeps piling up while the service is down, which makes recovery slow.
Microsoft said the cause was an issue during an earlier network capacity upgrade, not a cyberattack. It apologized on Friday and said it would publish a full report once its assessment is complete.
What Microsoft has said
Engineers began working on connectivity problems shortly before 1 p.m. ET on Thursday. Microsoft first blamed elevated load on part of its infrastructure, with some servers failing automated health checks and straining the rest.
"We are deeply sorry for the disruption this incident has caused our customers and partners," a Microsoft spokesperson said on Friday. The company said it had addressed the underlying issue and was restoring service to remaining customers and regions.
By Friday afternoon it reported "encouraging recovery progress" in Europe and improvement in North America. Some users may still see intermittent access problems or delayed email, it said. Microsoft shares traded largely flat on Friday.
Why email recovers slowly
Most cloud services act like a closed door. When they fail, users are locked out and stop generating work, so service often returns quickly once the bug is fixed.
Email works differently. It uses an older "store-and-forward" design meant to never lose a message, even when the destination is unreachable. People on Gmail or company servers could keep sending to affected accounts with no error message.
Their providers held those messages in queues and kept retrying. Millions of messages built up across the internet while Microsoft was down.
When engineers fix the fault, that backlog hits the restored service all at once. Think of a motorway crash: clearing the wreckage does not instantly end the tailback.
Prof James Ferryman of the University of Reading's computer science department said the part of Microsoft's servers that sets up secure connections was getting swamped. "You can't just turn it all back on at once," he said. "You have to bring it back bit by bit."
Delayed messages and wider impact
Microsoft extended the email timeout window, the period during which Outlook keeps trying to deliver delayed messages, to 48 hours. Delayed emails will carry the time they were delivered, not the time they were sent.
Schools, healthcare systems, businesses, courts and governments were hit. New Zealand's foreign ministry said its ability to receive emails was affected, including at embassies and consulates abroad. The UK's National Health Service said some services were disrupted but patients should attend appointments as normal.
Gergely Orosz, a former software engineer at Skype and Uber, said he "cannot recall" a business email outage taking this long to return to normal. Australian cyber-security expert Troy Hunt said Microsoft is "a massive part of the internet backbone" and the outage reminds us "how critical email still is."
Microsoft said on Friday that email queues were significantly reduced and approaching normal levels.
