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TL;DR
Microsoft 365 remained degraded at 08:35 UTC on Nov. 13, after an Exchange Online disruption that began the previous day. Microsoft says a patch has improved stability on part of its infrastructure and is being rolled out region by region; it has not identified the root cause.
Microsoft 365 remained in a service-degradation state at 08:35 UTC on Friday, Nov. 13, as Microsoft expanded a patch intended to stabilize Exchange Online servers after an outage that began Thursday. In an update at 08:06 UTC on incident EX1550543, Microsoft said servers were stable where the patch had been applied and that it was extending the fix region by region; the company has not named a root cause.
The disruption has affected users trying to reach Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as through REST connections, according to the incident information summarized by ThorstenMeyerAI.com. Because other Microsoft 365 services rely on Exchange Online, the reported effects also include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Microsoft Defender XDR portal, Purview and Planner. The precise impact can vary by service and user.
Microsoft’s updates describe a problem that persisted despite initial recovery steps. The company first cited elevated load across regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. It paused deployments, shifted traffic, restarted affected servers and changed its server-health checks. Microsoft later said a core process on affected servers was becoming overwhelmed; returned servers could become unresponsive again once they received traffic.
At 07:29 UTC Friday, Microsoft reported positive server-stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. Its 08:06 UTC update said the rollout was expanding systematically, beginning with regions in or approaching peak business hours. Microsoft also said it was not aware of malicious activity and would publish a Post-Incident Report after mitigation, according to the source material.
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 Spreads Across Workflows
The interruption matters beyond access to email because Exchange Online supports connected Microsoft 365 workflows. If mailbox connections fail, users may also have trouble with scheduling meetings, viewing calendars or using services that depend on Exchange Online. For businesses, that can interrupt routine coordination and access to work systems even when the issue is not affecting every Microsoft 365 feature in the same way.
The outage also has had effects outside Microsoft’s own services. ThorstenMeyerAI.com reported that OpenAI and Anthropic cited errors with their Microsoft 365 connectors. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the disruption. These examples show operational consequences, but they do not establish that every customer or connector was affected.
Reported outage counts offer a signal of the scale of complaints, not a count of people unable to work. Reuters, as published by The Korea Times, reported that Downdetector recorded more than 130,000 U.S. Outlook problem reports at a peak around 1 p.m. ET Thursday. Business Standard cited reports in 74 countries. Downdetector counts user reports, so those figures should not be read as verified totals of affected users.
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How the Outage Developed
Microsoft’s first public notice came at 17:54 UTC on Thursday, Nov. 12, describing reports of Exchange Online mailbox-access problems in the Americas under incident EX1550543. A copy of Microsoft’s service-health post on Cloud Admin Hub lists the incident start as 16:17 UTC. At 18:07 UTC, Microsoft said the issue might affect Microsoft 365 connectivity in any region.
Over the following hours, Microsoft described efforts to redistribute traffic, pause deployments and restart servers. It said a component responsible for processing server health might be involved, then reported that an alternative health-check method had allowed some servers to return to service. Later updates said those measures had not brought the expected relief and that affected servers could fail again under traffic. By 01:06 UTC Friday, Microsoft said a process involved in establishing secure connections was becoming overwhelmed and that it had begun reverting a recent network configuration change that correlated with the start of the impact.
A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC Thursday. BleepingComputer noted that Microsoft had not said whether it was related to EX1550543. The source material does not establish a connection between the two incidents.
“Servers are stable where the patch was applied.”
— Microsoft, in its 08:06 UTC Nov. 13 service-health update for EX1550543
Root Cause Still Unidentified
Microsoft has not disclosed a root cause, and it remains unclear which specific component or configuration initiated the failures. The company said a recent network configuration change correlated with the start of the impact and that it began reverting that change, but correlation alone does not establish it as the cause. Microsoft also reported that an applied change was not taking effect as expected.
The extent of the disruption is also not fully established in the available reporting. Downdetector figures are user reports rather than confirmed affected-user totals, and service effects may differ across regions, organizations and Microsoft 365 products. Microsoft’s statement that it is not aware of malicious activity is its current assessment, not a published final incident finding. The promised Post-Incident Report has not yet been provided.
Regional Patch Rollout Continues
Microsoft said it was expanding the patch region by region, starting with areas in or entering peak business hours. The immediate milestone is whether the rollout stabilizes more of the affected infrastructure and whether mailbox and connected-service access recovers for customers still experiencing errors. As of 08:35 UTC Friday, the status page continued to list service degradation, so the incident was not yet resolved.
Customers should check Microsoft’s service-health information and their organization’s support channels for current availability and instructions. If Outlook or a connected service is still failing, users can follow their organization’s established continuity procedures and avoid treating intermittent access as proof that all systems have recovered. Microsoft has said it will issue a Post-Incident Report once the problem is mitigated; its findings should clarify the cause, the scope and any further remediation.
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 improved stability on patched servers but had not declared the incident resolved.
Which services are reported as affected?
The main issue concerns Exchange Online mailbox access through Outlook and REST connections. Reported knock-on effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner; the impact may vary.
What does Microsoft say caused the outage?
Microsoft has not named a root cause. Its updates describe unexpectedly unavailable servers, an overwhelmed process and a recent network configuration change that correlated with the incident’s start. The company says it is not aware of malicious activity.
What should users do while services are degraded?
Check Microsoft’s service-health updates and your organization’s support guidance. If access remains unreliable, use established continuity procedures; Microsoft’s patch rollout is ongoing and the company has not confirmed full recovery.
Source: ThorstenMeyerAI.com
