Latest Update — September 1, 2026
Microsoft says its mitigation is producing gradual improvements across affected Microsoft 365 services, with mail flow recovering for more Outlook and Exchange Online users. However, the outage is not yet fully resolved. Some users may continue to experience delayed email delivery and varying levels of disruption while recovery work continues. Microsoft is restarting targeted sections of affected infrastructure to ensure re-applied authentication components take effect, and backlogged messages may take additional time to arrive. No firm time for full recovery has been announced. Administrators should continue monitoring incidents EX1464935 and MO1465074 in the Microsoft 365 admin center.
Microsoft is also continuing to assess the scope of the outage and look for additional affected scenarios. Users have reported delayed or failed emails, authentication errors and intermittent problems accessing mailboxes and Exchange Online services.
Microsoft Outlook and Exchange Online services are gradually recovering after a widespread Microsoft 365 outage disrupted email delivery, sign-ins, mailbox searches and several business cloud services on Monday, August 31, 2026. Microsoft says a problem involving its core authentication configuration contributed to the disruption, while engineers continue mitigation work across affected infrastructure.
The problems began Monday and quickly generated thousands of reports from people unable to send or receive messages, access mailboxes or sign in to Microsoft 365 services.
Microsoft initially tracked the Exchange Online disruption under incident EX1464935. After confirming that the authentication problem affected additional Microsoft 365 products, the company opened broader incident MO1465074.
Is Microsoft Outlook still down?
Microsoft says service conditions are improving gradually, but recovery is not yet consistent for every affected user. Email delivery has started returning across parts of the infrastructure, while some customers may continue to experience delays or intermittent failures.
Mailbox search can remain affected even after users regain access to Outlook. This means someone may be able to open their inbox and receive new messages while searches or other dependent functions continue to respond slowly or return incomplete results.
A previous Microsoft Outlook login outage in April 2026 also caused authentication-related access problems, although the circumstances and scope of the two incidents are separate.
What caused the Microsoft 365 outage?
Microsoft’s investigation identified an issue involving authentication components used across its cloud environment. The company later said a misconfiguration was preventing those components from being deployed correctly to part of the affected infrastructure.
Authentication systems verify user access to cloud services. When that shared layer fails, the impact can spread beyond a single Outlook application and affect several Microsoft 365 products at the same time.
Engineers developed a remediation strategy, tested it on a limited section of infrastructure and then expanded the mitigation as results improved. Microsoft has also restarted targeted infrastructure to help the re-applied authentication components take effect.
Which Microsoft 365 services were affected?
Exchange Online remained the most heavily affected service, but Microsoft confirmed broader degradation involving OneDrive for Business, SharePoint Online, Microsoft Teams, Microsoft Purview and Microsoft Defender XDR.
Exchange Online users could experience delayed or failed messages, authentication errors, incomplete searches and problems with administration tools. Other Microsoft 365 services could show access, synchronization or dependent-function failures.
Microsoft experienced another multi-service disruption earlier this year when a Microsoft 365 outage affected Outlook, Teams and other workplace services, illustrating how shared cloud dependencies can disrupt several products at once.
Outlook outage reports surged into the thousands
Downdetector recorded a sharp increase in Outlook complaints as the August 31 disruption developed. Reports rose from only a few dozen to more than 6,000 in a short period, with receiving email, app problems and login failures among the main issues reported.
Those figures should not be treated as Microsoft’s confirmed number of affected customers. Downdetector measures reports submitted by users, so the total number of impacted accounts may differ significantly.
Why emails may remain delayed during recovery
Regaining access to Outlook does not necessarily mean every delayed message will arrive immediately. Messages waiting while mail flow was disrupted can remain in processing queues as Microsoft restores affected systems.
This can create uneven recovery within the same organization. One employee may begin receiving messages normally while another continues to experience delays, authentication failures or search problems.
Because the issue is on Microsoft’s service side, repeatedly reinstalling Outlook, resetting passwords or changing account settings is unlikely to fix the underlying problem and may create unnecessary troubleshooting work.
How Microsoft is restoring services
Microsoft has been expanding its mitigation across affected environments while restarting targeted sections of infrastructure. The company says these actions are producing gradual improvements, particularly to mail flow.
Engineers are continuing to monitor sections that have not accepted the re-applied authentication components as quickly as expected. Residual impact can therefore remain in search and other downstream functions even as basic email delivery improves.
What should Outlook users do now?
Users still experiencing problems should check Microsoft’s official Microsoft 365 service status page. Business and enterprise administrators can also review the Microsoft 365 admin center for detailed information under EX1464935 and MO1465074.
If Outlook starts working but an expected email has not appeared, users should allow time for delayed mail to move through the system before changing account settings. Organizations relying on Outlook for urgent communication may temporarily use another approved communication channel where appropriate.
Microsoft 365 recovery remains in progress
Microsoft says its mitigation measures continue to improve service conditions, but users may still see varying levels of disruption and mail delays while recovery is completed.
The company has not provided a firm public time for full restoration. Until Microsoft formally closes the incidents, temporary problems involving email delivery, mailbox search and other dependent Microsoft 365 functions may continue for some users.
Updated September 1, 2026: This article reflects the latest available information about Exchange Online incident EX1464935 and the wider Microsoft 365 incident MO1465074.
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