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.
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How this story unfolded
3 events from the most recent confirmed update back to the earliest known activity.
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.
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.
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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Microsoft Fixes Outlook and Exchange Online Email Access Disruptions
Microsoft moved to resolve two separate email access problems affecting Outlook and Exchange Online users. In Exchange Online, a newly introduced **virtual account** change intermittently blocked some users from accessing cloud mailboxes through Outlook mobile apps and the new Outlook for Mac, prompting Microsoft to classify the issue as a service outage under `EX1256020`. After infrastructure restarts failed to restore access, the company identified the change as the root cause and began disabling it across affected environments. Microsoft also fixed a classic Outlook bug that caused Gmail and Yahoo accounts to stop synchronizing, triggering errors `0x800CCC0F` and `0x80070057` after users stopped receiving sign-in prompts. The company said the service-side fix was deployed, but some users could continue seeing sync failures until their OAuth token expires, such as after a password change. Microsoft published a temporary workaround to force a new sign-in prompt and noted it is still investigating other Outlook-related problems, including Exchange Web Services group creation failures and a Teams Meeting Add-in issue that can make classic Outlook unusable.
Apr 28, 2026
Microsoft cloud service disruptions affecting Microsoft 365, Exchange Online, and Windows Update/Store
Microsoft reported multiple **service-impacting incidents** across its cloud ecosystem. Administrators in **North America and Canada** experienced an outage and degraded performance in the **Microsoft 365 admin center**, with some users also unable to access the *M365 app* or raise support tickets; Microsoft said it was analyzing telemetry, usage patterns, and **CPU utilization**, and reviewing user-provided **HAR files** to isolate the root cause. Separately, **Exchange Online** quarantined legitimate messages after an updated **URL rule** incorrectly marked some URLs as phishing, disrupting email flow for affected customers while Microsoft worked to release quarantined mail and unblock legitimate URLs. In another disruption, Microsoft attributed **Windows Update** and **Microsoft Store** failures/timeouts (notably impacting Windows 11 users) to a **utility power interruption** at a **West US datacenter**, which cascaded into issues with **Azure storage clusters** supporting content delivery; backup power engaged and power was later stabilized, but service recovery required additional remediation beyond restoring electricity.
Mar 21, 2026
Microsoft 365 and Teams Outages Due to Infrastructure Issues
Microsoft Teams experienced widespread outages, with users across the United States, Europe, and other regions reporting delays in sending messages and problems with other service functions. Microsoft acknowledged the issue publicly, stating that they were investigating the cause and observing signs of recovery, but did not initially provide a root cause or timeline for full restoration. The outage disrupted communication for many organizations relying on Teams for collaboration and messaging. Separately, a significant outage affected Microsoft 365 services—including Teams, Outlook, OneDrive, and the Copilot AI assistant—in Japan and China. This disruption was traced to a critical routing misconfiguration in Microsoft's infrastructure, which isolated healthy systems and led to intermittent login failures, degraded performance, and app loading errors. Microsoft confirmed that the incident was not the result of a cyberattack and reported that engineers had rebalanced traffic to restore service, with no data loss or security breaches identified. The outages caused notable business disruption in the affected regions, particularly for organizations dependent on Microsoft’s cloud ecosystem for daily operations.
Mar 21, 2026