🔍 Read the full analysis: Microsoft 365 Outage Day Two: What’s Known, What To Watch on ThorstenMeyerAI.com
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TL;DR
Microsoft’s status page still listed a Microsoft 365 service degradation at 08:35 UTC on Nov. 13, after an outage that began the previous day disrupted Exchange Online and related services. Microsoft reported improved stability on some servers after a patch and said it was expanding the patch region by region, but had not disclosed the root cause.
Microsoft 365 remained affected by a service degradation at 08:35 UTC on Friday, Nov. 13, as Microsoft expanded a patch intended to stabilize Exchange Online servers. In its latest update, at 08:06 UTC, Microsoft said the patch had produced stable servers where applied; it had not identified or disclosed the root cause of the outage, which began the previous day and disrupted email and connected services.
The incident, tracked by Microsoft as EX1550543, affects access to Exchange Online mailboxes through Outlook on the web, desktop and mobile, as well as REST connections, according to the source report. Because other Microsoft 365 products rely on Exchange Online, reported effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Microsoft Defender XDR portal, Purview and Planner. The precise impact can vary by service and user.
Microsoft’s updates describe a changing diagnosis. It initially reported 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, redirected traffic, restarted servers and changed its server-health checks. It later said a core process on affected servers was becoming overwhelmed; returned servers could become unresponsive again after receiving traffic.
At 07:29 UTC Friday, Microsoft reported “positive results for server stability” 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 showed service degradation at 08:35 UTC, so the improvement did not mean the incident was resolved.
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
Email Disruption Spreads Across Workflows
The disruption matters beyond access to inboxes. When Exchange Online is unavailable or unstable, users can also lose access to scheduling features and other services that depend on it. That can delay meetings, interrupt internal coordination and affect organizations whose day-to-day work relies on Microsoft 365.
The incident has also had effects beyond Microsoft’s own products. The source report says OpenAI and Anthropic reported errors with their Microsoft 365 connectors. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage, according to the report. Those examples show how a cloud service incident can reach connected tools and business schedules, though they do not establish the total number of affected organizations.
Reported outage counts need care. Reuters, in a report published by The Korea Times, said Downdetector recorded more than 130,000 U.S. Outlook problem reports near a peak around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported complaints in 74 countries. Downdetector figures represent user reports, not verified counts of people affected; they indicate reporting volume, not the outage’s precise reach.
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How the Outage Developed
The first public notice came at 17:54 UTC on Nov. 12, when Microsoft’s 365 Status account said it was investigating reports of Exchange Online mailbox access problems in the Americas. A copy of Microsoft’s service-health post on Cloud Admin Hub lists the incident start as 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect connectivity for users in any region.
During the evening and overnight, Microsoft described efforts to redistribute traffic, pause deployments and restart servers. It said a subset of servers had returned to service after an alternative health-check method, but those efforts did not provide the expected relief. 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 incident’s start. Correlation alone does not establish that the change caused the outage.
A separate Teams incident, tracked as TM1550488, was marked fully resolved at 17:09 UTC Thursday, according to the source report. Microsoft has not said whether that shorter incident was related to EX1550543. Media reports cited in the source said service problems continued through parts of the Asian business day and into early European hours.
“Returned servers “can become unresponsive again once they begin receiving traffic.””
— Microsoft, service-health update at 23:59 UTC on November 12
Root Cause and Full Recovery
The root cause remains undisclosed. Microsoft has described unavailable servers, overwhelmed processes and a recent network configuration change that correlated with the start of the impact, but the updates supplied do not establish a definitive cause. The company said it was not aware of malicious activity; that statement is not a complete account of what caused the failure.
It is also unclear how many users and organizations remain affected, which regions or Microsoft 365 features have recovered, and how quickly the patch will reach all relevant infrastructure. Downdetector reports show complaints rather than confirmed affected-user totals. Microsoft has said it plans to publish a Post-Incident Report after the problem is mitigated.
Patch Rollout and Status Updates
Microsoft’s immediate next step is to continue expanding the patch region by region, prioritizing areas in or approaching peak business hours, according to its 08:06 UTC update. The company will need to confirm whether the patched servers remain stable under normal traffic and whether other regions and dependent services recover.
Users and administrators should treat the incident as ongoing until Microsoft changes the service-health status and reports that recovery is complete. The next useful milestones are a further update on the rollout, confirmation of service restoration, and the promised Post-Incident Report explaining the cause and response. The source report says its account would be updated as Microsoft posts new information.
Key Questions
Is the Microsoft 365 outage over?
No. The Microsoft status page still listed a service degradation at 08:35 UTC on Nov. 13. Microsoft reported improvement on patched servers, but had not declared the incident resolved.
Which services are reported as affected?
The main issue involves Exchange Online mailbox access through Outlook and REST connections. Reported effects also include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner; impacts may differ by service and user.
What caused the outage?
Microsoft had not identified a definitive root cause in the updates summarized here. It described server availability problems and an overwhelmed process, and said a recent network configuration change correlated with the start of the impact. It also said it was not aware of malicious activity.
What is Microsoft doing to restore service?
Microsoft said a patch improved stability on a portion of its infrastructure and that it was expanding the patch region by region, beginning with areas in or entering peak business hours.
How many people are affected?
A confirmed total is not available. Downdetector recorded more than 130,000 U.S. Outlook problem reports near a reported peak, but those are user reports, not a verified count of affected people.
Source: ThorstenMeyerAI.com
