🔍 Read the full analysis: Microsoft 365 Outage: Answers To Key Questions And Steps To Take on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained degraded at 08:35 UTC on Nov. 13, with Exchange Online access problems disrupting Outlook and related services. Microsoft said a patch was improving server stability and that it was expanding deployment region by region; it has not identified the root cause.
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 affected connected services, including Outlook and Teams calendar features. Microsoft has not named the underlying cause.
In its latest update, posted at 08:06 UTC under incident EX1550543, Microsoft said servers were stable in areas where it had applied a patch and that it was expanding the fix systematically, region by region. The company said it was prioritizing regions that were in or entering peak business hours. At 07:29 UTC, Microsoft had reported positive results for server stability after applying what it described as an upstream authentication and routing configuration component patch to part of its infrastructure.
The outage has affected access to Exchange Online through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the incident updates summarized by ThorstenMeyerAI.com. Services that rely on Exchange Online have also experienced problems, 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 with their Microsoft 365 connectors, while Workhorse Group rescheduled its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage.
Microsoft’s explanation developed over several updates. It first cited elevated load across regions, then said the strain was not caused by increased traffic but by servers becoming unexpectedly unavailable. The company paused deployments, redistributed traffic, restarted servers and changed its server-health checks. It later said a core process on affected servers was becoming overwhelmed. Earlier attempts to return servers to service did not hold: Microsoft reported that some 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
Disruption Across Connected Work Tools
The outage matters because Exchange Online supports more than email. When mailbox access fails, users may also lose or have trouble using features tied to the service, such as calendar scheduling and integrations with other workplace products. This can interrupt routine communication and coordination across organizations, even where other Microsoft 365 features continue to work.
The effects are not limited to Microsoft’s own interfaces. Reports of errors in third-party Microsoft 365 connectors show how disruption to a core cloud service can reach other software that depends on it. The reported postponement of Workhorse Group’s earnings call is a concrete example of an organization changing a scheduled business activity. The scale of impact for any individual customer will depend on which services and connection methods it uses.
Downdetector figures cited in reports give an indication of complaints, not a verified count of affected people. Reuters, in a report published by The Korea Times, said the site recorded more than 130,000 U.S. Outlook problem reports near a peak around 1 p.m. Eastern on Thursday. Business Standard, citing Downdetector, reported reports from 74 countries. Those figures should not be read as the number of users who lost access.
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How the Service Failure Developed
Microsoft’s first public notice came at 17:54 UTC on Nov. 12, when its Microsoft 365 Status account said it was investigating reports of Exchange Online mailbox access problems through multiple connection methods in the Americas. The service-health record, as reproduced by Cloud Admin Hub, gives the incident start time as 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect connectivity for users in any region.
Over the evening, Microsoft reported attempts to rebalance traffic and restore servers. At 20:19 UTC, it said it had not identified a recent change that correlated with the start of the impact, while investigating whether failed automated health checks originated in a component that processes server health. By 22:09 UTC, it said a core process on affected servers was becoming overwhelmed and causing capacity loss. In a 01:06 UTC update on Friday, Microsoft said a process responsible for establishing secure connections was overwhelmed and that it had begun reverting a recent network configuration change that correlated with the incident.
A separate Teams incident, TM1550488, was declared fully resolved at 17:09 UTC on Thursday. BleepingComputer reported that Microsoft had not said whether that incident was related to the Exchange Online outage. The two should not be treated as the same event based on the information available.
“Servers are stable where a patch was applied, and the company is expanding the patch region by region.”
— Microsoft, service-health update at 08:06 UTC, Nov. 13
Cause and Full Recovery Still Unknown
Microsoft has not disclosed a root cause or explained why the affected server processes became overwhelmed. Its updates describe server unavailability, failed health checks, secure-connection processing and a configuration component patch, but they do not yet provide a complete account of how those elements produced the outage.
The service remained listed as degraded at 08:35 UTC, and Microsoft had not said when patch expansion would finish or when all affected customers should expect normal service. The company said there was no indication of malicious activity. That is Microsoft’s current assessment, not a detailed public forensic report. The full number of affected users and organizations is also unknown; outage-reporting site counts measure submitted reports, not confirmed users.
It is also not clear whether the separate Teams incident earlier on Thursday was connected. Microsoft has not publicly established a link between the two records.
Watch for Restoration and Microsoft’s Report
Microsoft’s immediate next step is to continue expanding the patch region by region and monitor server stability as restored infrastructure receives traffic. Customers should check Microsoft’s service-health dashboard or their organization’s administrator for current availability, since the status may differ across regions and services. As of the latest information used here, Microsoft had not declared the incident resolved.
For users who still cannot connect, practical steps include checking service status before changing account or device settings, trying another supported Outlook connection method if available, and asking an IT administrator whether local guidance is in place. Organizations may need to use established backup communication procedures for time-sensitive work. These steps do not repair Microsoft’s cloud service, and users should avoid treating a temporary improvement in one app as proof that all connected services are back.
Microsoft has promised a Post-Incident Report after mitigation. That report is expected to provide a fuller account of the cause and response, but its publication timing and findings had not been announced in the updates summarized by ThorstenMeyerAI.com.
Key Questions
Is the Microsoft 365 outage over?
No. Microsoft 365 was still listed as experiencing service degradation at 08:35 UTC on Nov. 13. Microsoft said its patch was stabilizing servers where applied and that deployment was expanding.
Which Microsoft services have been affected?
The reported problem centers on Exchange Online mailbox access, affecting Outlook on the web, desktop and mobile and REST connections. Connected features and services have also experienced disruption, including Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner.
What should I do if Outlook is still unavailable?
Check Microsoft’s service-health information or your organization’s IT updates, then follow any local guidance. If available, you can try another supported access method or use established backup communication channels for urgent work. The outage is on Microsoft’s service side, so changing a password or repeatedly reinstalling an app may not resolve it.
Has Microsoft said what caused the outage?
No. Microsoft has described unavailable servers and overwhelmed processes, and it is applying a patch to an authentication and routing configuration component. It has not identified a final root cause and says it will publish a Post-Incident Report after the issue is mitigated.
Was the outage caused by a cyberattack?
Microsoft said it had no indication of malicious activity. The company has not published its full post-incident analysis, so its statement should be understood as its current assessment rather than a complete public explanation of the failure.
Source: ThorstenMeyerAI.com
