🔍 Read the full analysis: Microsoft 365 Outage Persists Into Day Two: A User’s Guide on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained degraded at 08:35 UTC on November 13, after Exchange Online problems disrupted email and connected services since Thursday. Microsoft reported improved server stability on patched infrastructure and was expanding the patch region by region, but had not identified the root cause.
Microsoft’s Microsoft 365 outage remained active at 08:35 UTC Friday, more than 16 hours after the company first reported Exchange Online access problems on Thursday. Microsoft said a patch had produced positive server-stability results on part of its infrastructure and that it was expanding the fix region by region; the company had not disclosed the root cause.
The incident, tracked as Exchange Online record EX1550543, began at 16:17 UTC Thursday, according to a copy of Microsoft’s service-health notice cited by Cloud Admin Hub. Microsoft’s first public post followed at 17:54 UTC and described reports of users unable to access Exchange Online mailboxes through multiple connection methods in the Americas. At 18:07 UTC, the company warned that Microsoft 365 connectivity could be affected in any region.
Microsoft’s updates describe a sequence of server and capacity problems. The company initially cited elevated load across several regions, then said that load was not caused by increased traffic: servers had unexpectedly become unavailable, straining the remaining infrastructure. Microsoft paused deployments, moved traffic, restarted affected servers and changed how server health was checked. Those measures did not provide lasting relief; the company later said servers could become unresponsive again after receiving traffic.
On Friday, Microsoft reported better results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. In its 08:06 UTC update, it said the rollout was expanding systematically, starting in regions at or approaching peak business hours. The status page still listed the service as degraded at 08:35 UTC, so Microsoft had not declared the incident 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 Microsoft 365
For affected customers, the outage reaches beyond inbox access. Microsoft says the Exchange Online issue affects connections through Outlook on the web, desktop and mobile, as well as REST connections. Services that rely on Exchange Online may also be impaired, including Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Microsoft Defender XDR portal, Purview and Planner.
The disruption can affect work that depends on receiving messages, arranging meetings or using connected Microsoft tools. It has also had reported effects outside Microsoft’s own services: OpenAI and Anthropic reported errors with their Microsoft 365 connectors, while Workhorse Group moved its third-quarter earnings call from November 12 to November 16 because of the outage, according to the source report. Those examples show the potential reach, but do not establish that every customer or integration is affected.
Scale estimates should be read carefully. Reuters, in a report published by The Korea Times, cited more than 130,000 Downdetector reports of Outlook problems in the United States at the peak around 1 p.m. ET Thursday. Business Standard cited reports from 74 countries. Downdetector figures count user submissions, not verified affected people, and the available accounts do not establish how many users lost access.
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How Thursday’s Outage Developed
Microsoft’s public updates traced the incident from a regional Exchange Online problem to a broader Microsoft 365 connectivity warning. At 18:35 UTC Thursday, the company said part of its infrastructure had elevated load across multiple regions. It later said the load followed unexpected server unavailability rather than a surge in traffic, and that a process involved in server health checks could be contributing to failures.
By late Thursday, Microsoft said a core process on affected servers was becoming overwhelmed and reducing capacity. An overnight update identified a process responsible for establishing secure connections as a problem, and said the company had begun reverting a network configuration change that correlated with the incident’s start. Microsoft also reported that an attempted change was not working as expected. On Friday, it reported positive stability results after patching part of the infrastructure.
A separate Teams incident, tracked as TM1550488, was declared fully resolved at 17:09 UTC Thursday, according to Microsoft. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543. It should not be treated as part of the continuing Exchange Online outage without further confirmation.
“The elevated load isn’t driven by an increase in traffic, but by a number of servers being unexpectedly unavailable.”
— Microsoft, in its 19:31 UTC update on November 12
Root Cause and Recovery Remain Open
Microsoft had not named a root cause as of 08:35 UTC Friday. Its updates describe overwhelmed server processes, failures in automated health checks and a network configuration change that correlated with the outage, but they do not establish a final causal explanation. The company said there was no indication of malicious activity; that statement does not identify what caused the technical failure.
The status page continued to show service degradation, and the company had not said how long the regional patch rollout would take or when all affected users would regain access. It is also unclear how many customers remain affected, whether every listed connected service has the same level of disruption, and whether the separate Teams incident was connected. Microsoft said it would publish a Post-Incident Report after mitigation.
Microsoft Expands the Regional Patch
Microsoft said it was expanding the patch region by region, prioritizing regions in or entering peak business hours. The next immediate indicator will be whether the status page changes from service degradation to a resolved state and whether Microsoft reports that stability holds as more traffic returns to patched infrastructure.
Customers should check Microsoft’s service-health updates for the latest status rather than assume that one service’s recovery means all Microsoft 365 features are working normally. The company has not announced a completion time. After the incident is mitigated, Microsoft has promised a Post-Incident Report; that report is expected to provide a fuller account of the cause and response, but no publication date was given.
Key Questions
Is Microsoft 365 back online?
Not fully, according to Microsoft’s status page as of 08:35 UTC on November 13. It still listed service degradation, although Microsoft reported improved stability on some patched servers.
Which services are affected?
The incident centers on Exchange Online mailbox access through Outlook on the web, desktop, mobile and REST connections. Microsoft also warned of possible effects on services that depend on Exchange Online, including Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner.
What caused the outage?
Microsoft had not confirmed a root cause. Its updates described unexpectedly unavailable servers and an overwhelmed process involved in establishing secure connections, and referred to a network configuration change that correlated with the incident’s start.
Is this a cyberattack?
Microsoft said it had no indication of malicious activity as of its 04:10 UTC update Friday. The company had not released a final explanation of the outage.
When will service be fully restored?
Microsoft had not provided a restoration deadline. It said at 08:06 UTC Friday that it was expanding the patch region by region; the service remained listed as degraded at 08:35 UTC.
Source: ThorstenMeyerAI.com
