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.
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How this story unfolded
6 events from the most recent confirmed update back to the earliest known activity.
Microsoft resolves Outlook.com outage and tells iPhone users to reauthenticate
Microsoft said it resolved a widespread Outlook.com service degradation on April 28, 2026, after users worldwide experienced intermittent sign-in failures, account sign-outs, and 'too many requests' errors. After service health returned to normal, the company instructed iPhone users to manually re-enter credentials in the iOS Mail app to restore access to Outlook and Hotmail accounts.
Microsoft reopens Exchange Online mailbox incident after continued impact
Microsoft said the Exchange Online mailbox access issue previously tracked as EX1256020 was marked resolved on April 1, 2026, but was later reopened under incident EX1268771 after affected tenants continued reporting intermittent access problems. The company said it was restarting the Notification Broker service on affected infrastructure while continuing root-cause analysis and work to prevent recurrence.
Microsoft identifies Exchange Online root cause and rolls back change
Microsoft determined that a newly introduced virtual account change in Exchange Online was causing the mailbox access issues and began disabling the change across affected environments after infrastructure restarts did not resolve the problem.
Microsoft deploys fix for Outlook Gmail/Yahoo sync bug
Microsoft said it deployed a service-side fix on Friday for the classic Outlook bug affecting Gmail and Yahoo synchronization, though some users could continue seeing issues until their OAuth token expired. The company also shared a temporary workaround to force a new sign-in prompt.
Exchange Online change starts blocking some mailbox access
Beginning on Thursday, some Exchange Online users were intermittently blocked from accessing cloud mailboxes through Outlook mobile apps and the new Outlook for Mac. Microsoft later tracked the incident as EX1256020 and classified it as a service outage.
Outlook sync failures begin for Gmail and Yahoo accounts
Microsoft said a classic Outlook issue started causing Gmail and Yahoo accounts to stop synchronizing on February 26, 2026, with affected users seeing errors such as 0x800CCC0F and 0x80070057 and no longer receiving sign-in prompts.
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Microsoft asks iPhone users to reauthenticate after Outlook outage
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Open sourceMicrosoft still working to fix Exchange Online mailbox access issues
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Open sourceMicrosoft Resolves Outlook Gmail And Yahoo Sync Errors In Microsoft 365 Service - gHacks Tech News
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Open sourceMicrosoft fixes bug causing Classic Outlook sync issues with Gmail
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Open sourceMicrosoft Exchange Online service change causes email access issues
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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.
Mar 21, 2026
Microsoft 365 Service Incident and Separate Windows/Outlook Update Issues
Microsoft reported a service incident impacting **Microsoft 365** core services, with users experiencing connectivity issues and service degradation across **Exchange Online**, **Microsoft Teams**, and the broader M365 suite. The incident was tracked as `MO1220495`, with Microsoft stating it was still in the *investigating/diagnostic* phase and providing no estimated time to resolution; organizations were directed to monitor the Microsoft 365 Service Health Dashboard for tenant-specific impact details. Separately, Microsoft published guidance for a client-side stability issue where the classic **Outlook desktop** app can freeze/hang after installing recent Windows security updates (notably `KB5074109`, and also `KB5073724`), particularly affecting POP accounts and scenarios where Outlook `PST` files are stored on cloud-backed storage such as **OneDrive**. Recommended mitigations included using webmail, moving `PST` files off OneDrive, or uninstalling the problematic updates while Microsoft investigates. A third item describing “Microsoft data breach” and “zero-day vulnerabilities” is largely a repackaged Patch Tuesday/vulnerability roundup and does not substantively align with the M365 service incident or the Outlook-freeze regression.
Mar 21, 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