🔍 Read the full analysis: What We Know About The Microsoft 365 Outage On Day Two on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained in service degradation status at 08:35 UTC on Nov. 13, after an Exchange Online outage that began the previous day disrupted email and connected services. Microsoft reported stable servers where it applied a patch and said it was expanding the patch region by region; the cause remains unknown.
Microsoft 365 remained in service degradation on Friday morning, Nov. 13, as Microsoft expanded a patch intended to stabilize Exchange Online servers affected by an outage that began the previous day. In an update at 08:06 UTC, Microsoft said servers were stable where the patch had been applied and that it was rolling it out region by region; it had not identified the root cause.
The incident, tracked as EX1550543, has disrupted access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the source account. Services that depend on Exchange Online have also been affected, 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 described elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. Microsoft paused deployments, shifted traffic, restarted affected servers and changed how server health was checked. It later reported that a core process on affected servers was becoming overwhelmed and that servers could become unresponsive again after receiving traffic.
At 07:29 UTC Friday, Microsoft reported positive server-stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. Its 08:06 update said the rollout was expanding systematically, beginning with regions at or entering peak business hours. The status page still listed the incident as a 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
Email Disruption Spreads Across Work Tools
The outage reaches beyond inbox access because several workplace services rely on Exchange Online. Problems with calendars and meeting scheduling can interfere with coordination, while outages affecting collaboration, security and compliance tools may limit other routine business work. The exact impact will differ by user, region and service.
The disruption also had reported effects beyond Microsoft’s own products. 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, citing the outage. These examples show practical consequences, but they do not establish the total number of organizations or users affected.
Some reported scale figures require care. Reuters, in a report published by The Korea Times, said Downdetector recorded more than 130,000 U.S. Outlook problem reports around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported reports from 74 countries. Downdetector measures user reports, not verified affected users, so those figures indicate complaint volume rather than a confirmed count of people without service.
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How the Outage Developed Overnight
Microsoft’s first public post came at 17:54 UTC Thursday, Nov. 12, saying it was investigating reports of Exchange Online mailbox access problems in the Americas. A service-health post reproduced by Cloud Admin Hub lists the incident start as 16:17 UTC. At 18:07 UTC, Microsoft said connectivity issues might affect users in any region.
Microsoft’s updates described several recovery attempts. It redistributed traffic, paused deployments and restarted servers. At 21:00 UTC Thursday, the company said an alternative health-check method had allowed some affected servers to return to service. Later updates said that had not brought the expected relief: servers could fail again when traffic resumed, and a process responsible for establishing secure connections was becoming overwhelmed.
Overnight, Microsoft said it was reverting a recent network configuration change that correlated with the start of the impact, but later reported that a change it had applied was not taking as expected. At 04:10 UTC Friday, it said there was no indication of malicious activity. A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC Thursday; BleepingComputer reported that Microsoft had not said whether it was connected to EX1550543.
“Servers are stable where the patch was applied, and the patch is being expanded region by region.”
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Root Cause and Full Recovery Still Unknown
Microsoft has not named a root cause, and its updates describe investigation findings rather than a final technical explanation. It said it had not identified a recent change correlated with the start of the impact, then said a network configuration change correlated with the outage and that it had begun reverting that change. The source material does not establish whether that configuration change caused the incident.
It is also not yet clear how many users remain affected, which regions or services have recovered, or how quickly the patch will reach the full infrastructure. The service-health status remained degraded at 08:35 UTC. Microsoft said it was not aware of malicious activity; that statement is not a final root-cause finding. The company has promised a Post-Incident Report after the problem is mitigated.
Patch Rollout and Microsoft’s Final Report
Microsoft’s stated next step is to continue expanding the patch region by region, prioritizing areas at or entering peak business hours. Users and organizations should consult Microsoft’s service-health updates for changes to EX1550543; the source information does not give a timetable for full recovery.
After mitigation, Microsoft has said it will publish a Post-Incident Report. That report is expected to provide more detail on the cause and response, though its publication timing and contents have not been specified. Until then, the confirmed status remains an active service degradation with improving stability reported on the portion of infrastructure already patched.
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 reported stability on patched servers but was continuing the rollout.
Which services have been affected?
The reported disruption centers on Exchange Online mailbox access through Outlook and REST connections. Connected services reported as affected include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner. The impact may vary by user and region.
What caused the outage?
The root cause has not been identified publicly. Microsoft has described unavailable servers, an overwhelmed process and a network configuration change that correlated with the incident. It has not confirmed a definitive cause.
Is Microsoft investigating a cyberattack?
Microsoft said it was not aware of malicious activity. The company has not published its final incident findings, so that statement should not be treated as a completed root-cause report.
When will service be fully restored?
Microsoft has not provided a full-restoration deadline. It said it was expanding the patch region by region and plans to publish a Post-Incident Report after the issue is mitigated.
Source: ThorstenMeyerAI.com
