🔍 Read the full analysis: Microsoft 365 Outage Continues Into Its Second Day: What To Do on ThorstenMeyerAI.com
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TL;DR
Microsoft’s status page still listed a Microsoft 365 service degradation at 08:35 UTC on Friday, Nov. 13, after Exchange Online problems began Thursday. Microsoft reported improved server stability after applying a patch to part of its infrastructure and said it was expanding the patch region by region; it has not identified the root cause.
Microsoft 365 remained degraded as of 08:35 UTC Friday, Nov. 13, after users began reporting access problems with Exchange Online the previous day. 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, but the service had not been declared restored and the root cause remains unknown.
The incident, tracked by Microsoft 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 source report. Services that depend on Exchange Online may 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 extent of disruption can vary by service and user.
Microsoft’s latest update, posted at 08:06 UTC Friday in the Exchange Online incident record, said servers were stable in areas where a patch had been applied. The company said it had started expanding the patch systematically, beginning with regions in or approaching peak business hours. At 07:29 UTC, Microsoft had described the stability results as positive after applying an upstream authentication and routing configuration component patch to part of its infrastructure.
Recovery has been uneven. Microsoft said earlier that servers brought back into service could become unresponsive again after receiving traffic. The company also reported that a process responsible for establishing secure connections was becoming overwhelmed and preventing affected servers from processing requests. It has not publicly named a definitive cause. Microsoft said it was not aware of malicious activity and plans to publish a Post-Incident Report after mitigation.
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 disruption reaches beyond inbox access because Exchange Online supports several connected Microsoft 365 functions. If mailboxes are unavailable or slow, users may also face problems scheduling meetings, viewing calendars or using other services that rely on the same infrastructure. For workplaces that use Microsoft 365 for routine communications and coordination, even partial outages can delay work and complicate customer and staff communication.
The incident has also had effects outside Microsoft’s own products. The source report 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. Those examples show that the consequences may extend to services and business events that depend on Microsoft 365, though they do not establish that every user or connected service is affected.
Reports on outage-tracking services offer an indication of public complaints, not a verified count of affected customers. Reuters, in a report published by The Korea Times, cited more than 130,000 U.S. Downdetector reports about Outlook problems near 1 p.m. ET Thursday. Business Standard cited reports from 74 countries. Downdetector counts user submissions, so neither figure should be read as the number of people who lost access.
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From Thursday Reports to Friday Patch
Microsoft’s first public notice came at 17:54 UTC Thursday, Nov. 12, when its Microsoft 365 Status account said it was investigating reports of users unable to access Exchange Online mailboxes through multiple connection methods in the Americas. A service-health copy cited by the source report put the incident’s start at 16:17 UTC. At 18:07 UTC, Microsoft said the issue might affect connectivity in any region.
Microsoft initially described elevated load across regions, then clarified that the load was not caused by increased traffic. It said some servers had become unexpectedly unavailable, putting strain on the remaining infrastructure. The company paused deployments, redistributed traffic, restarted servers and changed the method used to check server health. Later updates said those steps had not brought the expected relief and that affected servers could fail again under traffic.
At 01:06 UTC Friday, Microsoft said it had begun reverting a recent network configuration change that correlated with the start of the impact. It later reported that a change was not taking as expected. By 07:29 UTC, the company was reporting improved stability after applying a patch to part of its infrastructure. A separate Teams incident, tracked as TM1550488, had been marked fully resolved at 17:09 UTC Thursday; the source report says Microsoft has not established whether it is related to EX1550543.
“Servers are stable where a patch was applied, and the patch expansion has begun systematically, region by region.”
— Microsoft, in its 08:06 UTC Nov. 13 Exchange Online service-health update
Cause and Recovery Scope Remain Open
Microsoft has not identified the root cause or said how long it expects the full recovery to take. Its updates describe unavailable servers, an overwhelmed process involved in secure connections, and a recent network configuration change that correlated with the impact. Those details explain what the company observed and what it is investigating, but they do not establish a final cause.
It is also unclear how many users remain affected, which regions have received the patch, and whether all linked Microsoft 365 services are recovering at the same pace. Downdetector submissions are user reports rather than a count of affected people, and the service-specific effects may differ. Microsoft’s statement that it has no indication of malicious activity is not a published root-cause finding.
Watch for Regional Recovery Updates
Microsoft’s stated next step is to expand the patch region by region, starting with areas in or approaching peak business hours, and continue monitoring server stability. The status page and the EX1550543 service-health record are the primary places to check for changes to the incident’s scope and recovery status. A return to service in one region should not be taken as confirmation that all users or dependent services are restored.
Microsoft has said it will publish a Post-Incident Report once the issue is mitigated. That report is expected to provide more detail about the cause and response, but the company has not given a publication time in the source material. Until Microsoft updates the status, the outage should be treated as ongoing.
Key Questions
Is the Microsoft 365 outage over?
No. Microsoft’s status page still listed a service degradation at 08:35 UTC on Nov. 13. The company reported better stability in patched areas, but had not declared the incident resolved.
Which Microsoft 365 services are affected?
The incident centers on Exchange Online mailbox access through Outlook and REST connections. Microsoft 365 functions that depend on Exchange Online, including Teams calendars and meeting scheduling, may also be affected; the source report also lists parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner.
What should users do while the outage continues?
Check Microsoft’s service-health information for the current status of incident EX1550543 and follow your organization’s IT guidance. The source material does not provide a confirmed user-side workaround, so it would be misleading to promise that restarting an app or switching devices will resolve the underlying service issue.
Has Microsoft said what caused the outage?
Not yet. Microsoft has described server availability problems and an overwhelmed process involved in secure connections, and said a network configuration change correlated with the start of the impact. It has not published a definitive root cause.
When will Microsoft publish a full explanation?
Microsoft said it plans to issue a Post-Incident Report after mitigation, but it has not provided a date or time for that report.
Source: ThorstenMeyerAI.com
