🔍 Read the full analysis: Microsoft 365 Outage: What We Know, What Microsoft Says, What’s Next on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 was still experiencing service degradation at 08:35 UTC on Nov. 13, after an outage that began Thursday disrupted Exchange Online and related services. Microsoft said a patch improved server stability on part of its infrastructure and that it was expanding the patch region by region; the company has not identified a root cause.
Microsoft 365 remained in service degradation at 08:35 UTC on Friday, Nov. 13, as Microsoft expanded a patch intended to stabilize infrastructure behind an outage affecting Exchange Online and connected services. In an 08:06 UTC update for incident EX1550543, Microsoft said servers were stable where the patch had been applied; it has not named the underlying cause.
The disruption began Thursday, Nov. 12, and left many users unable to reach Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections. Microsoft’s status notices said the issue could affect Microsoft 365 connectivity across regions. Services that rely on Exchange Online also experienced problems, including Teams calendar and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s explanation developed over a series of updates. It first cited 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, redistributed traffic, restarted affected servers and changed its approach to server health checks. It later said a core process on affected servers was becoming overwhelmed, reducing capacity.
Those steps did not resolve the incident: Microsoft said servers returning to service could become unresponsive again once they received traffic. At 07:29 UTC Friday, the company reported positive stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. At 08:06 UTC it said it had started expanding the patch systematically, beginning with regions in or entering peak business hours. The status page still listed 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
Disruption Reaches Connected Work Tools
The outage matters beyond access to email because Exchange Online supports functions across Microsoft 365. When mailboxes or related connections fail, organizations may also lose access to calendars, meeting scheduling and other tools that depend on the service. That can interrupt routine work across teams and regions, even when a particular application is not itself the source of the fault.
There were reported effects outside Microsoft’s own applications. OpenAI and Anthropic both reported errors with their Microsoft 365 connectors, according to the source report. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage. These examples show that disruption to a widely used cloud service can affect external integrations and scheduled business activities as well as Microsoft 365 users.
Reports from service-monitoring sites indicate substantial user frustration, but they are not a count of people affected. Reuters, in a report published by The Korea Times, said Downdetector showed more than 130,000 Outlook problem reports in the United States at the peak, around 1 p.m. ET Thursday. Business Standard reported complaints in 74 countries, citing Downdetector. Those figures measure submitted reports, not verified outages or unique affected users.
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How the Incident Developed
Microsoft’s first public notice came at 17:54 UTC Thursday, when its Microsoft 365 Status account said it was investigating mailbox-access problems in the Americas. A copy of the service-health notice on Cloud Admin Hub lists the incident start as 16:17 UTC. At 18:07 UTC, Microsoft said the problem could affect connectivity in any region.
During Thursday evening, Microsoft said it was moving traffic away from affected infrastructure and restarting servers. It also investigated whether automated health checks were causing servers to be marked unavailable. At 21:00 UTC it said an alternative health-check method had allowed some servers to return to service, but later updates described capacity loss and servers becoming unresponsive under traffic.
At 01:06 UTC Friday, Microsoft said a process responsible for establishing secure connections was becoming overwhelmed and that it had begun reverting a recent network configuration change that correlated with the start of the impact. The company later said a change was not taking as expected. It stated at 04:10 UTC that it had no indication the incident resulted from malicious activity. A separate Teams incident, TM1550488, was marked fully resolved Thursday at 17:09 UTC; Microsoft has not said whether that issue was related.
“Servers are stable where a patch was applied.”
— Microsoft, service-health update at 08:06 UTC, Nov. 13
Root Cause and Recovery Remain Open
Microsoft has not identified or publicly named a root cause. Its updates have described unavailable servers, failed health checks, an overwhelmed process for secure connections and a network configuration change that correlated with the impact. Those details outline the investigation, but they do not establish a final cause.
The full scope and duration of the remaining disruption were also unclear as of 08:35 UTC. Microsoft had not said when the patch expansion would be complete or when all affected services would return to normal. Its statement that it was not aware of malicious activity is the company’s assessment at that time, not a published incident investigation. Microsoft said it would issue a Post-Incident Report after mitigation.
Downdetector figures cited in coverage should be read as user reports rather than confirmed counts of affected people. Microsoft has not provided a total number of impacted users, organizations or regions in the source material available for this update.
Microsoft Continues Regional Patch Rollout
Microsoft said it was expanding the patch region by region, starting with areas in or entering peak business hours. The immediate milestone is whether patched servers remain stable as they take on traffic and whether the rollout allows affected services to recover. The company had not supplied a completion time as of 08:35 UTC.
Users and administrators should check Microsoft’s service-health notices for current availability and further instructions, since the status may change as the patch reaches additional infrastructure. Microsoft has said it plans to publish a Post-Incident Report once the issue is mitigated; that report should provide a fuller account of the cause, impact and remediation. Until then, the incident remains developing.
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 was still expanding the patch.
Which services were affected?
The core reported issue involved Exchange Online mailbox access through Outlook and REST connections. Microsoft also said related services could be affected, including Teams calendars and scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner.
What caused the outage?
Microsoft has not announced a confirmed root cause. Its updates described servers becoming unavailable and an overwhelmed process involved in establishing secure connections, along with investigation of a network configuration change.
Did Microsoft say the incident was a cyberattack?
No. Microsoft said it had no indication of malicious activity. It had not published a final incident report or named the root cause in the updates cited here.
When will Microsoft 365 return to normal?
Microsoft had not given a recovery deadline as of 08:35 UTC Friday. It said it was expanding the patch region by region and planned to publish a Post-Incident Report after mitigation.
Source: ThorstenMeyerAI.com
