🔍 Read the full analysis: What Microsoft Says About The Ongoing Microsoft 365 Outage on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained in a degraded state at 08:35 UTC on Nov. 13, after an outage disrupted Exchange Online and connected services. Microsoft reported stable servers where it applied a patch and said it was expanding that patch region by region, but had not identified the root cause.
Microsoft 365 was still experiencing service degradation as of 08:35 UTC on Friday, Nov. 13, after an outage disrupted Exchange Online and other services used by businesses and individuals. Microsoft said its latest patch had produced stable servers in the portion of its infrastructure where it was applied, and that it was expanding the patch region by region; the company had not named the root cause.
The incident, tracked as Exchange Online case EX1550543, began at 16:17 UTC on Thursday, Nov. 12, according to a copy of Microsoft’s service-health notice published by Cloud Admin Hub. Microsoft first publicly reported problems at 17:54 UTC, saying users in the Americas were having trouble reaching Exchange Online mailboxes through multiple connection methods. At 18:07 UTC, it warned that Microsoft 365 connectivity could be affected in any region.
The disruption affected access through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the source report. Services that rely on Exchange Online were also affected, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner. OpenAI and Anthropic separately reported errors in their Microsoft 365 connectors, while Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage.
Microsoft’s explanation changed as its investigation progressed. It initially described elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. The company paused deployments, moved traffic, restarted servers and adjusted its server-health checks. It later said a core process on affected servers was becoming overwhelmed and that returned servers could become unresponsive again after receiving traffic.
In an update at 07:29 UTC Friday, Microsoft said it was seeing positive server-stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. At 08:06 UTC, in the EX1550543 service-health record, it said servers were stable where the patch had been applied and it was expanding the patch systematically, starting with regions in or entering peak business hours. The company’s status page still showed service degradation at 08:35 UTC.
Microsoft 365 outage · Nov 12–13, 2026 · times UTC
Down, rerouted, restarted, down again
How Microsoft described the outage, step by step, in its own status posts.
Server pool (schematic)
servingcarrying extra loadunavailablerestart
What Microsoft said
- 17:54Nov 12Mailbox access fails in the Americas
- 18:07“May affect” users “in any region”
- 18:35“Elevated load across multiple regions”
- 19:12All deployments paused, traffic moved, servers restarted
- 19:31Not more traffic: servers “unexpectedly unavailable”, the rest carry the load
- 21:00New health-check method: some servers back in service
- 23:59Returned servers “can become unresponsive again”
- 08:06Nov 13Patch stable where applied, now expanding region by region; still degraded
Hit
Exchange Online mail in Outlook, Teams calendars, SharePoint features, Microsoft 365 Copilot, Defender XDR portal, Purview and more
AI connectors
OpenAI and Anthropic reported errors in their Microsoft 365 connectors
Earnings call moved
Workhorse Group: from Nov 12 to Nov 16, citing the Microsoft outage
Sources: Microsoft 365 Status on X (Nov 12, 17:54–21:00 UTC); Microsoft service health EX1550543 (Nov 12, 23:59 UTC; Nov 13, 08:06 UTC) and status.cloud.microsoft MO1550821 (Nov 13, 07:29 UTC); Anthropic and OpenAI status pages; Workhorse Group press release, Nov 12, 2026. Server pool is a schematic, not real server counts.
Graphic: Powered by Thorsten Meyer AI
Outage Reaches Connected Work Tools
The incident matters because Exchange Online supports more than email. Problems with mailbox access can affect calendar coordination, meeting scheduling and connected Microsoft 365 tools, disrupting routine work across organizations. The reported impact on several linked services means users may encounter issues even when they are not directly trying to open Outlook.
The outage also had effects beyond Microsoft’s own products. Errors reported by OpenAI and Anthropic in their Microsoft 365 connectors show that services connected to Microsoft’s platform can also be affected. Workhorse Group’s decision to reschedule an earnings call provides a concrete example of an organization changing business plans during the disruption. Those reports do not establish that every customer or integration was affected.
Reported outage figures should be read carefully. Reuters, as published by The Korea Times, reported that Downdetector recorded more than 130,000 U.S. Outlook problem reports at the peak, around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported complaints from 74 countries. Downdetector counts user submissions, not verified affected people, so the figures indicate the volume and spread of reports rather than a confirmed number of users unable to work.
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How Microsoft’s Diagnosis Shifted
Microsoft’s public updates describe a sequence of attempted remedies rather than a confirmed explanation for the failure. On Thursday evening, it said it was redistributing connections, pausing deployments and restarting affected servers. It also said automated health checks were failing and that a specific component responsible for processing server health might be involved. A revised health-check method returned some servers to service, but that did not provide the expected relief.
By 22:09 UTC Thursday, Microsoft said an overwhelmed core process was causing capacity loss. At 01:06 UTC Friday, it specified that a process involved in establishing secure connections was becoming overwhelmed and stopping servers from processing requests. It also said it had begun reverting a recent network configuration change that correlated with the start of the incident. At 02:54 UTC, it reported that a change it had applied was not working as expected. The later patch update describes improved stability on a portion of the infrastructure, but does not itself identify what triggered the outage.
A separate Teams incident, tracked as TM1550488, was declared fully resolved by Microsoft at 17:09 UTC Thursday. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543. The two incidents should not be treated as connected without further confirmation.
“The elevated load isn’t driven by an increase in traffic, but by a number of servers being unexpectedly unavailable.”
— Microsoft, in its 19:31 UTC service update on November 12
Root Cause and Full Recovery Unknown
Microsoft has not identified a root cause, and it has not said how long the regional patch expansion will take or when all affected services will return to normal. Its updates have described server failures, overwhelmed processes, health-check problems and a network configuration change that correlated with the start of the incident. Those are details of the investigation, not a final account of what caused the outage.
Microsoft said at 04:10 UTC Friday that it had no indication the incident resulted from malicious activity. That statement reports the company’s current assessment; it does not identify the technical cause. The company has promised a Post-Incident Report after mitigation, but no report or final findings were available in the source material. It is also unclear whether every listed service experienced the same symptoms or whether the separate Teams incident was related.
The service-health status remained “Service degradation” at 08:35 UTC. The patch had been applied to only a portion of infrastructure, and Microsoft’s updates did not provide a confirmed count of affected customers, a percentage of capacity restored, or a completion estimate. Downdetector complaint totals likewise cannot establish how many people were unable to use the services.
Microsoft Expands Regional Patch
Microsoft’s stated next step is to expand the patch systematically across regions, beginning with areas in or entering peak business hours. It will need to monitor whether patched servers remain stable as they receive traffic and whether the repair restores access to Exchange Online and dependent services. Users and administrators should rely on Microsoft’s service-health updates for the latest status; the company had not supplied a firm restoration time in the information available at 08:35 UTC.
Once the incident is mitigated, Microsoft has said it will publish a Post-Incident Report. That report is expected to provide a fuller account of the cause and response, though its release date and contents have not been specified. Until then, the confirmed picture is limited: the outage is ongoing, some patched servers are reported stable, and the regional expansion is under way.
Key Questions
Is the Microsoft 365 outage over?
No. Microsoft’s status page still listed service degradation at 08:35 UTC on Nov. 13. The company reported improved stability on patched servers, but had not confirmed full recovery.
Which Microsoft services are affected?
The reported disruption centers on Exchange Online mailbox access through Outlook on the web, desktop and mobile, and REST connections. Reported knock-on effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Defender XDR, Purview and Planner. The exact impact can vary by service and user.
What does Microsoft say caused the outage?
Microsoft has not named a root cause. Its updates describe unexpectedly unavailable servers, an overwhelmed process involved in secure connections, health-check issues and a network configuration change correlated with the incident. A final explanation is pending.
Is Microsoft investigating a cyberattack?
Microsoft said at 04:10 UTC Friday that it had no indication of malicious activity. It has not attributed the outage to a cyberattack, and the technical cause remains under investigation.
When will Microsoft 365 be fully restored?
Microsoft had not given a full restoration estimate as of 08:35 UTC Friday. It said it was expanding a patch region by region and plans to publish a Post-Incident Report after the problem is mitigated.
Source: ThorstenMeyerAI.com
