TL;DR
Microsoft 365 remained degraded at 08:35 UTC on November 13, with users still reporting problems accessing Exchange Online and related services. Microsoft said a patch had produced stable servers where applied and that it was expanding the patch region by region. The company has not named the root cause.
Microsoft said it was expanding a patch region by region to address the Microsoft 365 outage, which remained listed as a service degradation at 08:35 UTC on November 13. In its 08:06 UTC update for incident EX1550543, the company said servers were stable where the patch had been applied; it has not identified the root cause.
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The incident began on Thursday, November 12. Microsoft’s first public notice, posted at 17:54 UTC by its Microsoft 365 Status account, said it was investigating reports of users unable to access Exchange Online mailboxes through multiple connection methods in the Americas. A later post, at 18:07 UTC, said the problem might affect Microsoft 365 connectivity in any region. A copy of Microsoft’s service health post on Cloud Admin Hub gives the incident start time as 16:17 UTC.
Microsoft’s updates described a changing response. At first, it cited elevated load across multiple regions. It later said the load was not caused by increased traffic, but by servers that had become unexpectedly unavailable. The company paused deployments, redistributed traffic, restarted servers and changed its method for checking server health. Overnight, Microsoft reported that some servers returning to service could become unresponsive again after receiving traffic.
On Friday, Microsoft reported positive server stability results after applying a patch to part of its infrastructure. The 08:06 UTC update said it had begun expanding the patch systematically, starting with regions in or entering peak business hours. Microsoft had not given a completion time, and its status page still listed service degradation at 08:35 UTC.
Services Beyond Outlook Are Affected
The outage affects more than mailbox access. Microsoft’s incident description and the source material identify problems for users reaching Exchange Online through Outlook on the web, desktop and mobile apps, as well as REST connections. Services that depend on Exchange Online, including Teams calendars and meeting scheduling, can also be affected. The reported service impact extends to parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
That reach can disrupt routine work across organizations, from reading email and arranging meetings to using connected productivity and security tools. OpenAI and Anthropic reported errors with their Microsoft 365 connectors, according to their status pages cited in the source material. Workhorse Group said it moved its third-quarter earnings call from November 12 to November 16 because of the outage. These examples show reported consequences; they do not establish that every customer or product experienced the same disruption.
Reports to Downdetector offer an indication of how many people were trying to report problems, but they are not a count of users who lost access. Reuters, as published by The Korea Times, reported more than 130,000 Outlook problem reports in the United States around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported reports from 74 countries. Those figures reflect user submissions, not independently confirmed totals of affected people.
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How Microsoft’s Response Changed
Microsoft’s initial public notice focused on reports of Exchange Online mailbox access failures in the Americas. Within minutes, the company widened its description to say the issue might affect connectivity in any region. At 18:35 UTC, it said part of its infrastructure was experiencing elevated load across multiple regions and that this was likely contributing to connectivity errors. At 18:48 UTC, it said it had started redistributing connection traffic across its worldwide infrastructure.
By 19:12 UTC, Microsoft said it had paused deployments, moved additional traffic away from affected infrastructure and restarted servers. At 19:31 UTC, it clarified that the elevated load did not reflect more traffic; instead, some servers were unexpectedly unavailable, leaving other servers to carry the load. At 21:00 UTC, it said a new health-check method had helped some servers return to service.
The recovery was not immediate. In an update posted around 23:59 UTC, Microsoft said returned servers could become unresponsive again once they began receiving traffic. A separate Teams incident earlier Thursday, tracked as TM1550488, was declared fully resolved at 17:09 UTC. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543.
“We’re investigating reports of users experiencing issues accessing Exchange Online mailboxes through multiple connection methods in the Americas.”
— Microsoft 365 Status account, 17:54 UTC on November 12
Root Cause Still Undisclosed
Microsoft has not named the root cause of the server failures or explained why the affected servers became unavailable. Its updates describe the symptoms and response, but do not establish what triggered the incident. The company said it was not aware of malicious activity; that statement does not identify a confirmed cause.
It was also unclear at 08:35 UTC how quickly the patch would reach all affected regions, when service would return to normal, or whether users would see further interruptions as traffic shifted. Microsoft had not provided a final count of affected customers or a full account of which services and regions were restored. It said it would publish a Post-Incident Report after the problem was mitigated.
Microsoft’s Regional Patch Rollout
Microsoft said it was continuing the region-by-region patch expansion, prioritizing regions in or approaching peak business hours. The company’s next practical milestone is a status update showing whether stability holds as patched servers handle traffic and the rollout reaches additional regions.
Customers can check Microsoft’s service health information for incident EX1550543 for updates on affected services and recovery. Microsoft has not announced when it expects the outage to be resolved. A Post-Incident Report is expected after mitigation, but the company has not given a publication date.
Key Questions
Is the Microsoft 365 outage over?
No. At 08:35 UTC on November 13, Microsoft’s status page still listed a service degradation. The company said servers were stable where its patch had been applied and that it was expanding the patch.
Which services are reported as affected?
The reported impact centers on Exchange Online mailbox access through Outlook and REST connections. Dependent or related services named in the source material include Teams calendars and scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Defender XDR, Purview and Planner.
What caused the outage?
Microsoft has not disclosed a root cause. It said the load was not caused by increased traffic, but by servers becoming unexpectedly unavailable. The company also said it was not aware of malicious activity.
What is Microsoft doing to restore service?
Microsoft paused deployments, redistributed traffic, restarted servers, changed its server health checks and applied a patch to part of its infrastructure. It said it was expanding that patch region by region.
When will Microsoft publish more detail?
Microsoft has not announced a resolution time or a date for its Post-Incident Report. It said it would publish the report once the problem is mitigated.
Source: Thorsten Meyer AI
