Microsoft Exchange Online Outage Disrupts Mailbox Access
Microsoft investigated and worked to mitigate an Exchange Online service disruption that prevented some customers from accessing mailboxes and calendars through multiple connection methods. The incident, tracked in the Microsoft 365 admin center as EX1253275, affected services including Outlook on the web, Outlook desktop, Exchange ActiveSync, and other Exchange Online protocols, with users also potentially impacted through clients relying on MAPI, IMAP, or EWS. Microsoft said engineering teams were analyzing the root cause and making service-side changes after identifying infrastructure that was not processing traffic efficiently.
The outage affected a subset of Exchange Online users globally, disrupting email, scheduling, and shared mailbox workflows for enterprise customers. Microsoft reported telemetry indicating recovery for some affected users while continuing to monitor service health for sustained restoration, although customer reports suggested access problems persisted during the response window. One report also noted a separate Microsoft 365 Copilot sign-in issue, but the core incident remained the Exchange Online mailbox-access outage and the resulting interruption to core Microsoft 365 communications services.
Timeline
Mar 16, 2026
Microsoft issues further public updates while continuing outage investigation
Microsoft published additional service health updates on March 16, 2026, including notices at 4:26 PM, 4:53 PM, and 7:49 PM IST, saying engineering teams were still working to identify the root cause and restore service. The company advised administrators to monitor the Microsoft 365 admin center and use unaffected access methods as temporary workarounds.
Mar 16, 2026
Microsoft reports telemetry shows recovery, but customers still see issues
Later the same day, Microsoft said telemetry indicated the Exchange Online issue was no longer occurring for affected users and that it was monitoring for sustained recovery. However, customers continued reporting mailbox access problems, and Office.com also displayed an error message.
Mar 16, 2026
Microsoft acknowledges Exchange Online mailbox access outage
Microsoft said it was investigating an Exchange Online service disruption preventing some customers from accessing mailboxes and calendars through multiple connection methods, including Outlook on the web, Outlook desktop, Exchange ActiveSync, and other Exchange Online protocols. The incident was tracked in the Microsoft 365 admin center as EX1253275 and was acknowledged at 06:42 UTC.
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