Microsoft Outlook users experienced a widespread service disruption on Monday as the company investigated an outage affecting Exchange Online, the cloud platform that powers business email, calendars, contacts and tasks.
Microsoft confirmed the issue via its Microsoft 365 Status account on X, noting that users were experiencing degraded functionality across several Exchange Online services. The company later said it had identified the cause and was testing a potential fix.
Microsoft Investigates Exchange Online Authentication Issue
Microsoft said the outage was linked to an issue involving an “authentication component.” The company began testing a remediation strategy on part of its infrastructure to determine whether the solution resolved the problem before expanding it more widely.
Users affected by the outage reported problems including delayed or failed email delivery, difficulties sending and receiving messages, mailbox search failures, authentication errors and other issues connected to Outlook workflows.
Microsoft provided additional updates via its service status posts, confirming that engineers were reviewing service telemetry and diagnostic data to isolate the source of the disruption.
Outage Reports Increased During Multi-Hour Disruption
The outage continued for several hours, with user reports increasing throughout the day. According to Downdetector, reports began appearing around 11:30 a.m. ET, with more than 5,000 reports recorded by around 2 p.m. ET.
Many users also reported problems directly on social media, as businesses relying on Outlook and Exchange Online experienced disruptions to normal communication and workflow.
The incident highlights the dependence many organisations have on cloud-based productivity services, in which disruptions can affect email communication and other essential business operations.
