🔍 Read the full analysis: Day Two Of Microsoft 365 Disruption: What Users Should Know on ThorstenMeyerAI.com
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TL;DR
Microsoft’s Microsoft 365 disruption continued into Friday, November 13, with Exchange Online access problems affecting Outlook and related services. The company reported improved stability on patched infrastructure and is expanding the patch region by region, but has not identified a root cause or declared the incident resolved.
Microsoft 365 remained disrupted as of 08:35 UTC Friday, November 13, after Exchange Online problems that began Thursday spread into a second day. Microsoft said a patch had improved stability on some servers and that it was expanding the fix region by region, but its status page still listed a service degradation and the company had not named the root cause.
The incident, tracked as EX1550543, has affected access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the source material’s account of Microsoft service notices. Services that rely on Exchange Online have also experienced problems, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s updates described a sequence of server and capacity problems. It initially cited 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, redistributed traffic and restarted servers. Those steps did not provide lasting relief: Microsoft later reported that servers returning to service could become unresponsive again under traffic, and that a core process on affected servers was becoming overwhelmed.
At 07:29 UTC Friday, Microsoft reported positive server-stability results after applying a patch to part of its infrastructure. In an update at 08:06 UTC, it said it had begun expanding the patch systematically, starting with regions at or approaching peak business hours. The source material also reports errors in Microsoft 365 connectors from OpenAI and Anthropic, and says Workhorse Group moved its third-quarter earnings call from November 12 to November 16 because of the outage.
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
Outage Disrupts Mail and Workflows
The disruption affects more than email. When Exchange Online is unavailable or unstable, organizations may also lose access to connected scheduling and collaboration functions, interrupting meetings and other routine work. The reported effects across Outlook, Teams and other Microsoft 365 services show how a problem in a shared service can ripple into tools used for different tasks.
The consequences can extend beyond Microsoft’s own products. The source material reports that two companies’ Microsoft 365 connectors encountered errors and that Workhorse Group postponed an earnings call. Those examples show possible operational effects, but they do not establish the total number of organizations or people affected. Users and businesses should distinguish Microsoft’s confirmed status updates from external disruption reports and avoid treating complaint counts as confirmed outage totals.
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How Thursday’s Incident Developed
Microsoft’s first public notice came at 17:54 UTC Thursday, when its Microsoft 365 Status account said it was investigating reports of problems accessing Exchange Online mailboxes through several connection methods in the Americas. The incident record reportedly gives a start time of 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect service connectivity in any region.
Through the evening and overnight, Microsoft reported attempts to shift traffic, restart affected servers and change the way server health was checked. It later said a process responsible for establishing secure connections was becoming overwhelmed. At 01:06 UTC Friday, Microsoft also said it had begun reverting a recent network configuration change that correlated with the start of the impact; a later notice said a change it had applied was not taking as expected. Microsoft separately stated there was no indication of malicious activity.
Reports cited in the source material suggest the disruption crossed business hours in several regions. Downdetector figures reported by Reuters and Business Standard reflected user submissions, not verified counts of people unable to work. A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC Thursday; the source material says Microsoft has not established whether it was related to EX1550543.
“We’re seeing positive results for server stability after applying an upstream authentication/routing configuration component patch to a portion of our infrastructure.”
— Microsoft, service update at 07:29 UTC on November 13
Root Cause and Full Recovery Unknown
The root cause remains unidentified. Microsoft’s updates described overwhelmed processes, server health-check failures and a network configuration change that correlated with the start of the incident, but the information provided does not establish which factor caused the outage or how they relate. Microsoft has not said how many customers, users or regions remain affected.
It is also unclear how quickly the patch will reach all affected infrastructure or whether stability will hold when patched servers receive normal traffic. Microsoft had previously said servers could become unresponsive again after returning to service. Its statement that it is not aware of malicious activity is not a final explanation of what happened. The status page still listed a degradation at the reported time, and no final recovery time had been given.
Watch for Regional Patch Updates
Microsoft said it would continue expanding the patch region by region, prioritizing regions in or entering peak business hours, and monitor server stability. Users should check Microsoft’s service health notices for changes to EX1550543 and follow their organization’s IT guidance; the available information does not give a reliable time for full restoration.
Microsoft has promised a Post-Incident Report after the problem is mitigated. That report is expected to provide further detail on the cause and response, but it was not available as of 08:35 UTC Friday. Until Microsoft marks the incident resolved and confirms recovery, the service status should be treated as developing.
Key Questions
Is the Microsoft 365 outage over?
No. As of 08:35 UTC on November 13, Microsoft’s status page still listed a service degradation. The company reported improvement on some patched servers but had not declared the incident resolved.
Which services have been affected?
The reported disruption centers on Exchange Online and Outlook. Microsoft 365 services that rely on Exchange Online have also experienced problems, including Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner.
What has Microsoft done to address the problem?
Microsoft said it paused deployments, redirected traffic, restarted affected servers and changed its server health-check approach. It later reported positive stability results after applying a patch and said it was expanding that patch across regions.
Has Microsoft identified the cause?
No root cause has been named. Microsoft described overwhelmed server processes and mentioned a network configuration change correlated with the incident, but its updates do not establish a definitive cause.
Was the outage caused by a cyberattack?
Microsoft said it was not aware of malicious activity. That is the company’s reported assessment during the investigation; it has not yet published its final incident report.
Source: ThorstenMeyerAI.com
