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TL;DR
Microsoft still listed a Microsoft 365 service degradation at 08:35 UTC on Nov. 13, after an outage that began the previous day disrupted Exchange Online and dependent services. The company said a patch improved server stability in part of its infrastructure and was being expanded region by region; the root cause remains unknown.
Microsoft’s Microsoft 365 outage was still ongoing as of 08:35 UTC on Friday, Nov. 13, with its status page listing a service degradation after widespread problems accessing Exchange Online began the previous day. Microsoft said a patch had produced positive server-stability results on part of its infrastructure and that it was expanding the patch region by region, but it had not identified the root cause.
The disruption, tracked as EX1550543, affects access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the supplied account of Microsoft’s service updates. Because other Microsoft 365 products rely on Exchange Online, reported effects extend to Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Defender XDR portal, Purview and Planner. The exact impact can vary by service and user.
Microsoft’s account of the response changed as it investigated. It first described elevated load across multiple regions, then said the problem was not caused by increased traffic but by servers unexpectedly becoming unavailable. The company paused deployments, redistributed traffic and restarted affected servers. It later reported that a core process on some servers was becoming overwhelmed and that servers could become unresponsive again after receiving traffic.
At 07:29 UTC Friday, Microsoft reported positive stability results after applying a patch to part of its infrastructure. In an 08:06 UTC update, it said it was expanding the patch systematically, beginning with regions at or entering peak business hours. Microsoft has not said how long that expansion or full service recovery will take.
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
How the Outage Disrupts Work
The incident reaches beyond inbox access because email, calendars and meeting scheduling are connected to work across Microsoft 365. People may be unable to retrieve messages or arrange meetings, while teams relying on affected services could face interruptions to collaboration, document workflows or security and compliance tools. Microsoft’s description does not establish that every listed service is unavailable to every customer; readers should check their own service access and administrator notices.
The outage has also had reported effects outside Microsoft’s own products. The source account says OpenAI and Anthropic reported errors with their Microsoft 365 connectors. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage. These examples illustrate how reliance on cloud services can affect connected tools and business plans, though they do not establish the full number of organizations affected.
For workers and administrators, the immediate priority is to avoid treating a service failure as a local account or device problem without evidence. Confirming the status through Microsoft’s service-health information and organizational IT channels can help teams distinguish an ongoing provider issue from an individual sign-in or connectivity problem.
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How Microsoft’s Response Evolved
Microsoft’s first public notice came at 17:54 UTC on Nov. 12, saying it was investigating reports of Exchange Online mailbox access problems in the Americas. The incident record cited in the source material gives a 16:17 UTC start time. At 18:07 UTC, Microsoft broadened its notice to say connectivity could be affected in any region.
During the evening and overnight, Microsoft described efforts to move traffic, restart servers and change how server health was checked. At 01:06 UTC Friday, it said a process responsible for establishing secure connections was becoming overwhelmed and that it had begun reverting a recent network configuration change that correlated with the incident’s start. It later said that change was not taking as expected. Microsoft has not said that the configuration change was the confirmed cause.
Downdetector figures cited in the source material show the volume of complaints, not a verified count of affected customers. Reuters, as published by The Korea Times, reported more than 130,000 U.S. Outlook problem reports at the Thursday peak; Business Standard cited reports from 74 countries. A separate Teams incident earlier Thursday was marked resolved, and the supplied account says Microsoft has not established whether it was related.
““initiated its expansion systematically””
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Cause and Recovery Timing Remain Unknown
Microsoft had not named a root cause as of the latest update in the source material. Its investigation mentioned server health checks, an overwhelmed secure-connection process and a recent network configuration change, but those details do not amount to a confirmed explanation. Microsoft said it was not aware of malicious activity; that statement is the company’s assessment, not an independently established finding.
It is also unclear how quickly the patch will reach all affected regions, whether every dependent service will recover at the same time, and whether users will see recurring problems as traffic returns. The service-health status remained degraded at 08:35 UTC, so recovery was not confirmed complete.
The reported Downdetector totals are user reports rather than verified counts of people or organizations without service. The precise number of affected customers, the regional distribution of continuing issues and the relationship, if any, to the separate Teams incident remain unclear in the supplied material.
Watch for Regional Recovery Updates
Microsoft said it was expanding the patch region by region, prioritizing areas in or entering peak business hours. Customers should monitor Microsoft’s service-health page and follow guidance from their organization’s IT administrator for updates on EX1550543 and the products they use. A listed improvement in one region or service does not by itself confirm full recovery elsewhere.
Microsoft has promised a Post-Incident Report after the problem is mitigated. That report is expected to provide further information about the cause and response, but no publication time was given in the source material. Until Microsoft changes the incident status, the outage should be treated as developing.
Key Questions
Is the Microsoft 365 outage over?
No. The status was still listed as a service degradation at 08:35 UTC on Nov. 13. Microsoft reported improved server stability in part of its infrastructure, but said it was still expanding the patch.
Which services may be affected?
The main reported issue is access to Exchange Online mailboxes through Outlook and REST connections. The source material also identifies possible effects on Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner. The impact may differ among users and services.
What should users do while recovery continues?
Check Microsoft’s service-health updates and your organization’s IT notices before assuming the issue is limited to your device or account. If a service is still unavailable, follow your workplace’s continuity procedures and wait for Microsoft or your administrator to confirm recovery. The source material does not provide a universal workaround.
Does Microsoft know what caused the outage?
Not yet, based on the latest supplied update. Microsoft described server availability, health checks, an overwhelmed process and a network configuration change under investigation, but had not confirmed a root cause.
When will Microsoft publish more details?
Microsoft said it would issue a Post-Incident Report after mitigation, but the source material gives no publication date. Its service-health updates remain the source for the recovery status in the meantime.
Source: ThorstenMeyerAI.com
