Microsoft is working to restore Outlook, Teams and other Microsoft 365 services after an Exchange Online outage that began on Thursday evening, East Africa Time. Some servers have returned to service, but Microsoft said on Friday that capacity remained below normal and recovery varied across affected services.
The first mailbox connectivity problems began at about 7:17 p.m. EAT on November 12, according to Microsoft’s incident reports, mirrored by the University of Pennsylvania. Microsoft is tracking the Exchange Online problem as EX1550543 and the wider disruption as MO1550821.
Which Microsoft 365 services were affected?
Outlook and Exchange Online. Some users could not open their work mailboxes through Outlook on the web, the desktop app or other clients that connect to Exchange Online. Microsoft also warned that email delivery could be delayed. Mail flowing between an organisation’s own servers and Exchange Online could be affected as well.
Microsoft Teams. The disruption hit features that depend on Exchange Online, including calendars and meeting scheduling. Microsoft also listed possible problems creating chats in organisations that use policies to restrict communication between certain groups.
Microsoft 365 Copilot. Some users could not load Copilot Chat or get a response. Even where the interface opened, Copilot could have trouble retrieving work information such as email, calendars and files.
SharePoint, Planner and administration tools. Microsoft’s wider advisory listed disruptions affecting SharePoint Online and reliability problems with some Planner operations. It also flagged problems loading certain Microsoft 365 admin centre pages and using features in Defender and Purview. Microsoft Graph requests for mail, calendar and contacts could time out, affecting other applications that rely on Microsoft 365 data.
The symptoms could vary within the same organisation. A user might be able to open Teams while still being unable to schedule a meeting, or regain access to Outlook before delayed messages arrived.
Why Microsoft’s first recovery attempts didn’t hold
Microsoft initially saw heavy load across several regions. Engineers later determined that a large number of servers had become unavailable, leaving the remaining infrastructure to handle more requests. Microsoft rerouted traffic and restarted affected servers, but some became unresponsive again once they started receiving requests.
In its Exchange Online advisory, Microsoft said a process responsible for establishing secure connections was becoming overwhelmed, causing affected servers to stop handling requests. Engineers tested a configuration patch on part of the infrastructure and reported better server stability. They then began rolling it out to more servers and returning traffic in stages.
Microsoft said it had seen no evidence of malicious activity associated with the incident. It plans to explain the underlying cause and the steps it will take to prevent a recurrence in a post-incident report.
The disruption reached businesses and public services
In Japan, the government said the outage had affected some of its IT infrastructure. The Philippines’ Supreme Court reported disruption to operations including email responses, according to the Associated Press.
In the United States, industrial technology company Workhorse Group moved its quarterly earnings call from November 12 to November 16, citing disruption from the Microsoft outage.
Is Outlook back up?
Microsoft’s Friday updates described gradual improvement, with some workloads still below normal capacity. Organisations can check EX1550543 and MO1550821 under Service health in the Microsoft 365 admin centre. If the admin centre is itself unavailable, Microsoft provides a public service health page.
For teams relying on Outlook or Teams for urgent work, the useful check is whether the specific function they need is back. A mailbox can load while delivery is still delayed, and Teams can open while calendar features are still recovering.
