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Microsoft confirmed an ongoing Exchange Online incident, tracked as EX1467029, that is delaying inbound and outbound messages involving external domains. Affected users have intermittently encountered “Server busy” errors across multiple mailboxes; Microsoft said anti-spam protections may be compounding delays for a subset of accounts while it analyzes service telemetry to isolate the issue.
Microsoft had not identified a root cause, the affected regions or user count, or a remediation timeline. The disruption follows the recently mitigated EX1464935 incident, which caused authentication, mailbox-search, and mail-delivery problems from August 31 through September 3; organizations relying on external email should account for delayed business communications, security alerts, and email-based MFA messages.
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Microsoft confirmed and investigated Exchange Online incident EX1467029, which delayed inbound and outbound email involving external domains and intermittently produced “Server busy” errors. The company said anti-spam protections might be compounding delays for some users while it analyzed telemetry to determine the cause and mitigation path.
Microsoft declared EX1464935 fully mitigated after testing and gradually deploying remediation across affected infrastructure.
Microsoft 365 experienced Exchange Online incident EX1464935, causing authentication failures, mailbox-search problems, and delayed message delivery. Microsoft later attributed the incident to a fault in a core authentication component shared across multiple Microsoft 365 services.
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Microsoft is investigating **Exchange Online incident `EX1464935`**, a service disruption causing Outlook and Exchange Online authentication failures, mailbox-operation errors, synchronization problems, and delayed or failed inbound and outbound email delivery. Administrators reported Outlook on the web access issues, failed searches, administrative-function disruptions, and mail-flow errors including `550 5.6.200 STOREDRV.Deliver; message is treated as poison.` Downdetector reports indicated that tens of thousands of users were affected, with organizations in the U.S. Southwest reporting particularly substantial impact while some tenants remained operational. Microsoft identified a shared failure pattern involving authentication and protocol connectivity and is reviewing telemetry to establish the root cause, affected scope, and remediation options. Exchange Online is the only service Microsoft has formally identified as affected; separate user reports involving Teams, Azure, Microsoft Store, and a distinct Teams VDI issue (`TM1463371`) have not been confirmed as related. Organizations should monitor the Microsoft 365 Service Health Dashboard, mail queues, delivery reports, and Exchange connectivity while the investigation continues.
Sep 3, 2026
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.
Jul 12, 2026
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.
Jun 29, 2026