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TL;DR
Microsoft 365 remained in service degradation status at 08:35 UTC on November 13, after an Exchange Online outage that began the previous day. Microsoft reported stable servers where it applied a patch and said it was expanding the fix region by region, but it had not identified the root cause.
Microsoft’s Microsoft 365 outage was still active at 08:35 UTC on November 13, after disrupting Exchange Online and connected services since the previous day. In an update at 08:06 UTC, Microsoft said servers were stable where it had applied a patch and that it was expanding the patch region by region; the company had not named the root cause.
The incident, tracked as EX1550543, affects access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the source material. Microsoft said the issue could affect Microsoft 365 connectivity in any region. Services that depend on Exchange Online have also experienced disruption, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s explanations developed as it investigated. It first reported elevated load across multiple regions, then said that the load was not caused by increased traffic but by servers unexpectedly becoming unavailable. The company paused deployments, redistributed traffic and restarted affected servers. It later said a core process on affected servers was becoming overwhelmed and that restarted servers could become unresponsive again after receiving traffic.
On November 13, Microsoft said it had seen positive stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. Its 08:06 UTC update said it had begun expanding that patch systematically, starting with regions at or entering peak business hours. The company has said it will publish a Post-Incident Report after the problem is mitigated.
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 outage disrupted connected work
The disruption reaches beyond inbox access because many workplace tools rely on Exchange Online for calendars, meeting scheduling or other functions. A user might be able to open one Microsoft 365 application while still finding a connected feature unavailable; the precise effects can vary by service and region as Microsoft works through its recovery.
The outage has also affected organizations outside Microsoft’s own products. The source material says OpenAI and Anthropic reported errors with their Microsoft 365 connectors. Workhorse Group moved its third-quarter earnings call from November 12 to November 16 because of the outage. These examples show how a disruption to a widely used cloud service can interfere with both internal work and services that connect to it.
For readers planning around the incident, Microsoft’s reports of stability on patched servers are a sign of progress, not confirmation that service has been restored everywhere. The service status remained degraded at 08:35 UTC, so organizations should treat availability as potentially uneven until Microsoft reports mitigation.
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From regional load to server failures
Microsoft’s first public notice came at 17:54 UTC on November 12, saying it was investigating Exchange Online mailbox access problems in the Americas. The incident record cited in the source material gives a start time of 16:17 UTC. At 18:07 UTC, Microsoft said the connectivity issue could affect users in any region.
Updates through the evening described traffic redistribution, paused deployments, server restarts and work on an alternative health-check method. Microsoft later said the affected servers’ secure-connection process was becoming overwhelmed. At 01:06 UTC on November 13, it also said it had begun reverting a recent network configuration change that correlated with the start of the impact, while cautioning at 02:54 UTC that a change it had applied was not taking as expected. The later patch update reported improved stability on a portion of the infrastructure.
Reports of the outage’s scale should be read carefully. The source material cites more than 130,000 U.S. Downdetector reports around 1 p.m. ET on November 12 and reports from 74 countries. Downdetector counts user submissions, not verified affected people, so these figures indicate reported complaints rather than the number of users unable to work. Microsoft also marked a separate, shorter Teams incident, TM1550488, resolved at 17:09 UTC on November 12; it has not said whether that incident was related.
“Servers are stable where a patch was applied.”
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Root cause and full recovery remain unknown
As of the latest status described, Microsoft had not identified or announced a root cause. Its updates refer to server health checks, an overwhelmed process responsible for secure connections, a network configuration change that correlated with the incident and a patch to an authentication and routing component. Those details describe the investigation and response; they do not establish a final cause.
It is also unclear how long the patch rollout will take, which regions or services remain affected, and when Microsoft will mark the incident resolved. The company said it was not aware of malicious activity, but that statement is not a final incident finding. The relationship, if any, between EX1550543 and the separate Teams incident has not been disclosed.
Downdetector submissions cannot establish the total number of affected users, and the source material does not provide a confirmed count from Microsoft. Availability may differ by region, application and connection method while the patch expands.
Microsoft continues regional patch rollout
Microsoft’s stated next step is to expand the patch systematically, beginning with regions in or entering peak business hours, and monitor server stability as traffic returns. The company has not provided a completion time in the updates described here. Users and administrators should consult Microsoft’s service-health information for current, service-specific updates rather than assume that a local recovery means the incident is over for everyone.
Organizations can plan around the uncertainty by checking whether email, calendars, meeting scheduling and connected services are working in their own environment, and by following existing continuity procedures if they are not. Microsoft has promised a Post-Incident Report after mitigation; that report may provide a fuller account of the cause and response. Until Microsoft confirms resolution, the status remains developing.
Key Questions
Is the Microsoft 365 outage over?
No. The status page still listed service degradation at 08:35 UTC on November 13. Microsoft reported stable servers where it applied a patch, but said it was still expanding the rollout.
Which Microsoft 365 services have been affected?
The incident centers on Exchange Online mailbox access, including Outlook through web, desktop, mobile and REST connections. Reported knock-on effects include Teams calendars and scheduling, parts of SharePoint Online, Copilot, the Defender XDR portal, Purview and Planner.
What caused the outage?
Microsoft had not announced a confirmed root cause. Its updates described unexpectedly unavailable servers and an overwhelmed process, and said a network configuration change correlated with the start of the impact. The company said it was not aware of malicious activity.
What should users do while service is disrupted?
Check Microsoft’s service-health updates and verify whether the particular apps and functions you rely on are available. If they are not, follow your organization’s existing continuity procedures; Microsoft had not given a time for full restoration.
Will Microsoft publish an explanation?
Microsoft said it would publish a Post-Incident Report after the issue is mitigated. The timing and contents of that report were not specified in the updates described here.
Source: ThorstenMeyerAI.com
