🔍 Read the full analysis: Microsoft 365 Outage: Causes, Company Updates, And What To Do on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained under a service degradation notice at 08:35 UTC on Nov. 13, after an Exchange Online outage disrupted email and connected services from the previous day. Microsoft says a patch has improved server stability in part of its infrastructure and is being expanded region by region; the root cause remains unknown.
Microsoft 365 remained in service degradation at 08:35 UTC on Friday, Nov. 13, as Microsoft expanded a patch intended to stabilize servers affected by an outage that began the previous day. The disruption has prevented many users from reaching Exchange Online mailboxes and has affected other services that rely on Microsoft 365, while Microsoft has not identified a root cause.
In an update at 08:06 UTC on the Exchange Online incident record EX1550543, Microsoft said servers were stable in areas where it had applied a patch and that it was expanding the change region by region. An earlier update, at 07:29 UTC, reported “positive results for server stability” after a patch to an upstream authentication and routing component on part of its infrastructure. The company said it was prioritizing regions in, or approaching, peak business hours.
The incident affects access to Exchange Online through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the source material. Reported knock-on effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner. The exact availability of individual features may vary as Microsoft works through the incident.
Microsoft’s explanations have changed as it investigated. It first cited elevated load across multiple regions, then said the load was not caused by increased traffic but by servers unexpectedly becoming unavailable. The company later described an overwhelmed process on affected servers, including a process responsible for establishing secure connections. Earlier restarts did not provide lasting relief: Microsoft said some returned servers became unresponsive again after receiving traffic.
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
How the Exchange outage spread
The outage matters beyond email because several Microsoft 365 tools depend on Exchange Online for connected functions, including calendars and meeting scheduling. When mailbox access or related infrastructure is disrupted, organizations may lose access to workflows that support communication, collaboration and security operations at the same time.
The effects have also reached organizations outside Microsoft’s direct service notices. OpenAI and Anthropic reported errors with their Microsoft 365 connectors, according to the source material. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage. These examples show how a cloud service disruption can affect connected products and scheduled business activity, though they do not establish the full scale of the impact.
Reports on outage-monitoring services provide an indication of user complaints, not a verified count of people affected. Reuters, as published by The Korea Times, reported that Downdetector recorded more than 130,000 Outlook problem reports in the United States around 1 p.m. ET on Thursday. Business Standard, citing Downdetector, reported reports from 74 countries. Those figures should not be read as the number of users unable to work.
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From Thursday reports to Friday patch
Microsoft’s first public notice came at 17:54 UTC on Thursday, Nov. 12, when its Microsoft 365 Status account said it was investigating problems accessing Exchange Online mailboxes through several connection methods in the Americas. The incident record, as reproduced by Cloud Admin Hub, gives a start time of 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect service connectivity in any region.
Over the following hours, Microsoft said it was redistributing traffic, pausing deployments, restarting affected servers and changing how server health was checked. At 22:09 UTC it said an overwhelmed core process was causing capacity loss. In an overnight update, it said a process involved in secure connections was becoming overwhelmed and that it had begun reverting a recent network configuration change that correlated with the impact. Microsoft later said a change it applied was not working as expected.
A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC on Thursday, according to Microsoft. BleepingComputer reported that Microsoft had not said whether that incident was related to the ongoing Exchange Online outage. The two should not be treated as the same event without further confirmation.
““We’ve initiated its expansion systematically.””
— Microsoft, in its 08:06 UTC update on incident EX1550543
Root cause and recovery remain open
Microsoft has not named the root cause, and its status page still listed the incident as service degradation at 08:35 UTC. The patch has produced stability in the portion of infrastructure where it was applied, but Microsoft was still expanding it. The company’s earlier reports that restarted servers could fail again under traffic mean the broader recovery cannot be assumed from the initial positive results.
It is also unclear how many users or organizations remain affected, which specific services are fully restored in each region, and when Microsoft expects the incident to be resolved. Downdetector figures measure submitted reports rather than confirmed affected users. Microsoft said it was not aware of malicious activity, but had not yet published a post-incident account explaining the failure or its cause.
Microsoft expands the regional fix
Microsoft said it would continue expanding the patch region by region, beginning with areas in or entering peak business hours, and monitor server stability as traffic returns. Users and administrators should check Microsoft’s service health notices for the current status of their affected services; the incident may progress differently across regions and products.
The next major account of the incident is expected after mitigation. Microsoft has promised a Post-Incident Report once the problem is mitigated. Until that report or a further status update is published, the cause, complete impact and final recovery timeline remain unconfirmed.
Key Questions
Is the Microsoft 365 outage over?
No. As of 08:35 UTC on Nov. 13, Microsoft’s status page still listed service degradation. The company said a patch was improving stability in part of its infrastructure and was being expanded.
Which Microsoft 365 services are affected?
The main reported issue is access to Exchange Online mailboxes through Outlook and REST connections. Reported knock-on effects include Teams calendars and scheduling, parts of SharePoint Online, Copilot, the Defender XDR portal, Purview and Planner; availability may vary.
What caused the outage?
The root cause has not been identified publicly. Microsoft has described servers becoming unavailable and an overwhelmed process that affected request handling, but has not provided a confirmed underlying cause.
Has Microsoft ruled out a cyberattack?
Microsoft said it had no indication of malicious activity. That is the company’s reported assessment, not an explanation of what caused the service failure.
Where can users check for updates?
Users and administrators can check Microsoft’s service health notices, including the Exchange Online record EX1550543. Microsoft said it plans to publish a Post-Incident Report after the problem is mitigated.
Source: ThorstenMeyerAI.com
