🔍 Read the full analysis: Microsoft 365 Outage Update: What Happened And What Comes Next on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained degraded at 08:35 UTC on Nov. 13, after an outage affecting Exchange Online and services that depend on it began the previous day. Microsoft reported improved server stability after a patch and said it was expanding the fix region by region; it has not identified the root cause.
Microsoft 365 remained in service degradation at 08:35 UTC on Friday, Nov. 13, as Microsoft expanded a patch intended to stabilize servers affected by an outage that began the previous day. In the latest update to incident EX1550543, posted at 08:06 UTC, Microsoft said servers were stable where the patch had been applied; the company had not named a root cause.
The incident has disrupted access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the status information summarized by ThorstenMeyerAI.com. 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. The precise impact may vary by service and user.
Microsoft’s explanation developed as it investigated. It first 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, restarted affected servers and changed its server-health checks. Later updates said a core process on affected servers was becoming overwhelmed, and that servers returned to service 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 begun expanding the patch systematically, starting with regions in or entering peak business hours. That indicates remediation was continuing; it does not establish that service had been restored for all customers.
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
Disruption Reaches Connected Work Tools
The outage matters because Exchange Online is not just an email destination: calendars, meeting scheduling and other Microsoft 365 functions rely on connected services and infrastructure. When mailbox access fails, organizations can also lose access to workflows that depend on it, even if those products are not themselves entirely offline. That can delay internal coordination and customer communications across regions and working hours.
The reported spillover extended beyond Microsoft’s own products. ThorstenMeyerAI.com said OpenAI and Anthropic reported errors in their Microsoft 365 connectors, though the source material does not specify the exact scope or duration of those errors. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage, an example of how service disruption can affect scheduled business activity.
Reports from Downdetector indicate the scale of user complaints, not a verified count of people affected. Reuters, in a report published by The Korea Times, said the site recorded more than 130,000 Outlook problem reports in the United States around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported complaints from 74 countries. Those figures should not be read as the number of users who lost access.
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From Thursday Mail Failures to Friday Patching
Microsoft’s first public notice came at 17:54 UTC on Thursday, Nov. 12, when its Microsoft 365 Status account said it was investigating reports of Exchange Online mailbox access problems in the Americas. A copied service-health notice cited by ThorstenMeyerAI.com placed the incident start at 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect connectivity in any region.
Over the evening, Microsoft described attempts to move traffic, pause deployments and restart servers. At 21:00 UTC Thursday, it said an alternative health-check method had allowed some affected servers to return to service. By 22:09 UTC, it said those actions had not brought the expected relief and identified an overwhelmed core process as a source of capacity loss. An overnight update said a process responsible for establishing secure connections was becoming overwhelmed; Microsoft also said it had begun reverting a network configuration change that correlated with the outage’s start.
A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC Thursday. BleepingComputer reported that Microsoft had not said whether it was related to EX1550543. The status timeline and service list in this account are based on the supplied report from ThorstenMeyerAI.com, which cited Microsoft updates and other news coverage.
“Servers are stable where a patch was applied, and the patch expansion is proceeding region by region.”
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Root Cause and Recovery Scope Remain Open
The root cause has not been disclosed. Microsoft’s updates described unavailable servers, overloaded processes and a network configuration change that correlated with the start of the impact, but the supplied material does not establish which underlying fault triggered the incident. Microsoft also said it had not identified a recent change correlated with the start of impact in an earlier update, before later describing the configuration change correlation.
It was not clear at 08:35 UTC which regions or customers had received the patch, how quickly expansion would proceed, or when Microsoft 365 would return to normal service worldwide. The status page still listed degradation. The relationship, if any, between the Exchange Online incident and the separately resolved Teams incident also remained unconfirmed.
Microsoft said it was not aware of malicious activity and promised a Post-Incident Report after the problem is mitigated. Until that report is published, the full technical cause, the complete duration of impact and any final account of affected services remain unsettled.
Microsoft Plans Further Regional Rollout
Microsoft’s next stated step is to continue expanding the patch region by region, prioritizing areas in or entering peak business hours. Customers should treat the incident as ongoing while the status page reports degradation; the 08:06 update described improving stability on patched infrastructure, not a universal recovery declaration.
Further status-page updates should clarify whether the patch is stabilizing additional servers and whether affected services are recovering across regions. Microsoft has said it will publish a Post-Incident Report after mitigation. That report is expected to provide a fuller account, but no publication time was given in the supplied material.
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. Microsoft reported stable servers where the patch had been applied, but said it was still expanding the fix.
Which services were affected?
The reported disruption centered on Exchange Online mailbox access through Outlook and REST connections. Related effects included Teams calendars and scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Defender XDR, Purview and Planner.
What caused the outage?
Microsoft has not named a root cause. Its updates described servers becoming unavailable and an overwhelmed process involved in establishing secure connections. The company also referred to a network configuration change that correlated with the incident’s start.
Was the outage caused by a cyberattack?
Microsoft said it had no indication of malicious activity. That is the company’s statement in a status update; a full post-incident account had not yet been published.
What happens next?
Microsoft said it would expand the patch region by region and continue monitoring server stability. It has promised a Post-Incident Report after the issue is mitigated, but has not given a publication date.
Source: ThorstenMeyerAI.com
