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TL;DR
Microsoft 365 remained in service degradation on Friday, Nov. 13, after Exchange Online problems that began the previous day disrupted email and connected services. Microsoft reported improved server stability after applying a patch to part of its infrastructure and said it was expanding the patch by region; it has not identified the root cause.
Microsoft 365 remained in service degradation as of 08:35 UTC on Friday, Nov. 13, after an Exchange Online outage disrupted access to email and connected services since Thursday. Microsoft said a patch had improved stability on some servers and that it was expanding the fix region by region, but the company had not named the root cause.
The incident is tracked as EX1550543. Microsoft’s first public update came at 17:54 UTC Thursday, reporting problems accessing Exchange Online mailboxes through multiple connection methods in the Americas. At 18:07 UTC, the company said the issue could affect Microsoft 365 connectivity in any region. The service health record places the incident’s start at 16:17 UTC.
Microsoft’s updates described a sequence of server and capacity problems. The company initially cited elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. It paused deployments, moved traffic, restarted servers and changed its server health-check approach. Later updates said a core process on affected servers was becoming overwhelmed and that some servers returned to service could become unresponsive again once they received traffic.
At 07:29 UTC Friday, Microsoft reported positive server-stability results after applying a patch to an upstream authentication and routing configuration component on part of its infrastructure. In the 08:06 UTC update for EX1550543, it said it had begun systematically expanding the patch, starting in regions in or entering peak business hours. The status page still listed 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 Failures Spread Across Microsoft 365
The disruption extends beyond people unable to open an inbox. Services that depend on Exchange Online can also be affected, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner. The practical impact varies by service and user, but failures can interrupt communications, scheduled work and access to business tools.
Other organizations reported knock-on effects. OpenAI and Anthropic reported errors with their Microsoft 365 connectors, according to the source report. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage. The incident illustrates how a problem in a widely used cloud service can affect organizations that rely on it as well as other products connected to it.
Scale figures require care: reports cited by Reuters and Business Standard came from Downdetector, which counts user-submitted reports rather than independently verified affected customers. Reuters, in a report published by The Korea Times, said reports of Outlook problems in the United States topped 130,000 at a peak around 1 p.m. ET Thursday. Business Standard cited reports from 74 countries. Neither figure establishes how many people lost access.
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From Regional Reports to a Wider Outage
Microsoft’s first public notice focused on Exchange Online access problems in the Americas. Within minutes, its status account said connectivity issues could affect users in any region. CNBC reported that email and other tools remained unavailable through much of the Asian business day and into the early European hours, showing how the disruption crossed working days in different time zones.
Microsoft’s account of the technical investigation shifted as it gathered evidence. On Thursday evening, it said automated health checks were marking servers unavailable and that a component responsible for processing server health might be involved. Later it reported that a process responsible for establishing secure connections was overwhelmed. At 01:06 UTC Friday, the company also said it had begun reverting a recent network configuration change that correlated with the start of the impact. These updates describe investigative findings, not a confirmed root cause.
A separate Teams incident, tracked as TM1550488, was declared fully resolved at 17:09 UTC Thursday. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543. It should not be treated as confirmation that the two events shared a cause.
“We have initiated its expansion systematically, starting with regions that are in or entering peak business hours.”
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Root Cause and Full Recovery Remain Unknown
Microsoft has not identified a root cause for EX1550543. Its updates have discussed unavailable servers, failed health checks, an overwhelmed process involved in secure connections and a network configuration change that correlated with the incident. The company has not said which, if any, of these findings explains how the outage began.
Microsoft said it was not aware of malicious activity. That is the company’s assessment, not a public forensic report. The status page still showed degradation at 08:35 UTC, and the latest patch expansion was underway; there was no confirmed restoration time or statement that all affected services and regions had recovered. The exact number of affected users is also unclear, and outage-report counts should not be read as a verified customer total.
Microsoft has promised a Post-Incident Report once the problem is mitigated. Until then, details about the cause, the full extent of service impact and whether all symptoms share the same technical source remain unconfirmed.
Watch Regional Patch and Status Updates
Microsoft’s immediate next step is to continue expanding the patch across regions and monitor server stability as infrastructure returns to service. Users and administrators should check the Microsoft 365 service health page for updates to incident EX1550543; the company’s status account has also posted updates. Recovery may vary by region and service while mitigation continues, so a reported improvement on patched servers does not by itself mean every user is back online.
For users still affected, practical steps include checking the official service status before spending time troubleshooting a local device or network, and retrying the affected service after Microsoft posts a recovery update. Organizations can use their established incident procedures and alternative communications or scheduling arrangements where available. Avoid treating third-party outage-report totals as confirmation of the status of a specific account or tenant.
Microsoft has not announced a resolution time. The next significant update will be whether regional expansion produces sustained stability and whether the service health record changes from degradation to recovery or resolution. A Post-Incident Report is expected after mitigation, but no publication date was given.
Key Questions
Is the Microsoft 365 outage over?
No resolution had been confirmed as of 08:35 UTC on Nov. 13. Microsoft’s status page still listed service degradation while the company expanded a patch across regions.
Which services may be affected?
The main reported issue involves Exchange Online mailbox access. Services that rely on it may also have problems, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Defender XDR, Purview and Planner. The impact may differ by service and user.
What should users do now?
Check the Microsoft 365 service health page for incident EX1550543 and follow updates from Microsoft. If the service is still listed as degraded, retry after a status update; use available alternative communications or scheduling arrangements if work cannot wait.
Does Microsoft know what caused the outage?
Not yet. Microsoft has described server availability, health-check and process problems, and a network configuration change that correlated with the incident, but it has not confirmed a root cause.
Was the outage caused by a cyberattack?
Microsoft said it was not aware of malicious activity. The company has not published a final incident investigation, so that statement should not be confused with a confirmed technical explanation for the outage.
Source: ThorstenMeyerAI.com
