Microsoft confirmed a widespread, multi-hour outage on Monday that disrupted Outlook and Exchange Online, causing delays and failures in email delivery, authentication errors, mailbox search problems, and other service issues. The company traced the disruption to an authentication component that also affected services beyond Exchange Online.
User reports began appearing at around 11:30 a.m. ET, according to Downdetector. By 2 p.m. ET, the outage-tracking service had recorded more than 5,000 reports, while users also reported problems on social media.
Microsoft Traces Problems to Authentication Component
Microsoft initially said it was investigating reports of Exchange Online problems before confirming the service disruption through its Microsoft 365 Status account. Exchange Online is Microsoft’s cloud-hosted platform for business email, calendars, contacts, and tasks.
At 12:43 p.m. ET, Microsoft said users could experience degraded functionality across several Exchange Online features while engineers reviewed service telemetry and diagnostic data. Affected users could encounter delays or failures when sending and receiving emails, mailbox search failures, authentication errors, and problems completing other mailbox operations.
Microsoft later said it had identified an issue involving an authentication component and developed a remediation strategy. The company began applying the proposed fix to part of its infrastructure to test whether it resolved the disruption before considering a wider deployment.
Further testing showed that the authentication problem was affecting services beyond Exchange Online. Microsoft continued adjusting its remediation approach as internal tests progressed.
Misconfiguration Investigated as Outage Continues
By later Monday, Microsoft said its investigation indicated that a misconfiguration might be preventing authentication components from deploying correctly to part of its infrastructure. Engineers were reviewing recent service changes to determine why the problem was occurring.
The outage remained unresolved as of 5 p.m. ET, more than five hours after Microsoft began investigating user reports. The company was still working on its remediation strategy at that point.
The disruption affected Outlook users who rely on Exchange Online for workplace communications and related functions. Outlook is part of Microsoft’s broader Microsoft 365 suite and is widely used for business email and calendar services.
Microsoft had not provided a final resolution time or detailed the full range of other services affected by the authentication issue as of its latest update on Monday.
Featured image credits: Wikimedia Commons
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