The World's Email Went Dark: Microsoft 365 Outage Locks Millions Out of Outlook, Teams and Copilot

Microsoft's email and workplace services went down across the world on Thursday, locking millions of users out of Outlook and disrupting Teams, SharePoint and Copilot in an outage that was still not fully fixed on Friday morning. The disruption began at 16:17 UTC on 12 November, when users in the Americas first found they could no longer reach their Exchange Online mailboxes, and within two hours Microsoft had widened the incident to cover users in any region. By Friday morning the company was reporting only gradual, uneven recovery, with restored servers failing again as soon as traffic returned to them, and it had given no time for full restoration.

The scale of the failure was visible within an hour. Downdetector, which tracks user-submitted problem reports, logged reports from 74 countries and territories, and Outlook reports in the United States peaked at 138,058 at around 1 p.m. Eastern Time on Thursday, according to Reuters. The numbers fell through the evening — to about 34,490 Outlook reports by nightfall — as some users reconnected, but Microsoft's own status page still listed the incident as "service degradation" in its 06:17 UTC update on Friday, and its 09:57 UTC update spoke only of "positive results for service stability and increased capacity". The company extended its email timeout window to 48 hours to preserve messages delayed by the outage.

Microsoft has said the outage was not a cyberattack. A company spokesperson told the Australian Broadcasting Corporation there was "no indication this is a cyber attack", and Microsoft executive Charles Lamanna said the same, with the company stating it was "not aware of any malicious activity" behind the incident. What it has described instead is an infrastructure failure: a large number of its own servers unexpectedly became unavailable after failing automated health checks, leaving the remaining infrastructure buckling under the load. A core process that establishes secure connections became overwhelmed, Microsoft said, even though overall traffic had not increased. The company is rebuilding a subset of servers using a previous configuration to test whether that stops them failing, and is reverting a recent network change that lines up with when the problems began.

The list of affected services kept growing as the day went on. Microsoft tracked the mailbox problem as incident EX1550543 and the wider disruption as advisory MO1550821, naming Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR, with Planner, To Do, Intune, Purview and Power BI also hit. Teams chat and meetings mostly kept working, but calendars, scheduling and creating new chats could fail, and security tools built on email — Defender for Office 365's Safe Links and Safe Attachments, quarantine and threat investigation — failed at times, leaving security teams partly blind during the incident. A separate, shorter Teams incident earlier on Thursday, tracked as TM1550488, ran from 9:45 to 10:53 a.m. Eastern and was resolved; Microsoft has not said whether the two are linked.

The disruption spilled beyond Microsoft's own products. Reuters reported that the outage hit connectors used by OpenAI's and Anthropic's AI services to reach Microsoft 365, and the US electric truck maker Workhorse Group postponed its third-quarter results announcement from 12 November to 16 November, citing business disruption from the outage. Hospitals, schools, police forces and parliaments were among the organisations affected in Britain, where GP surgeries and pharmacies reported being unable to reach email, and in South Africa businesses started Friday without email at all. For companies whose entire working day runs through Outlook, the outage was not an inconvenience but a halt: meetings unscheduled, invoices unsent, and customer service queues frozen while the world's most widely used business email system stayed dark.

Online, the reaction mixed dark humour with real frustration from the people paid to keep email running. A thread on r/technology sharing the BleepingComputer report passed 8,700 upvotes, while on r/sysadmin an outage thread drew more than 6,300 upvotes and 5,300 comments as administrators swapped workarounds — and another thread, noting that Microsoft owes customers money under its service-level agreement, passed 2,400 upvotes. What happens next turns on Microsoft's root-cause report, which the company has promised once the incident is closed: whether a routine change or a failing health-check system took down the servers, and what the company will change so that the failure of one part of its cloud does not take the world's email with it.