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TL;DR
Microsoft 365’s Exchange Online outage continued into Friday, Nov. 13, with Microsoft still listing service degradation at 08:35 UTC. Microsoft reported stable servers where it applied a patch and said it was expanding the patch region by region, but it has not identified the root cause.
Microsoft 365’s outage continued into Friday, with Microsoft’s status page still reporting service degradation at 08:35 UTC on Nov. 13. In an 08:06 UTC update for incident EX1550543, Microsoft said servers were stable where a patch had been applied and that it was expanding the patch region by region; the company has not disclosed the underlying root cause.
The disruption began Thursday, Nov. 12, and has affected access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to Microsoft’s incident updates. Microsoft warned that the problem could affect Microsoft 365 connectivity in any region. Because other services rely on Exchange Online, reported impacts also include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s account of the problem changed as its investigation progressed. The company first described elevated load across multiple 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 how server health was checked. Later updates said an overwhelmed core process was reducing capacity, and that returned servers could become unresponsive again when traffic resumed.
At 07:29 UTC Friday, Microsoft reported positive results for server stability after applying a patch to part of its infrastructure. Its 08:06 update said the patch rollout was proceeding systematically, starting with regions in or entering peak business hours. The status page nevertheless continued to list a degradation, so the improvement did not mean service had been fully restored.
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 Exchange Disruption Spreads
The incident matters beyond people unable to open email. Exchange Online supports connected Microsoft 365 functions, so a mailbox disruption can affect scheduling, collaboration and tools used to manage information and security. That can slow routine work and complicate coordination for organizations whose communications and workflows depend on the service.
There are also reported effects beyond Microsoft’s own products. OpenAI and Anthropic said their Microsoft 365 connectors were experiencing errors. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage, according to the source report. These examples show how an extended service interruption can affect integrations and business plans, though the full number of affected organizations is not known.
Outage-reporting figures offer an indication of user complaints, not a verified count of people affected. Reuters, as published by The Korea Times, reported that Downdetector recorded more than 130,000 U.S. Outlook problem reports near a peak around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported complaints from 74 countries. Downdetector counts reports submitted by users; the figures should not be read as confirmed numbers of disrupted users.
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From Thursday Reports to Friday Patch
The first public notice came at 17:54 UTC Thursday, when the Microsoft 365 Status account on X said it was investigating problems accessing Exchange Online mailboxes through multiple connection methods in the Americas. A copied Microsoft service-health post on Cloud Admin Hub gives the incident start time as 16:17 UTC. At 18:07 UTC, Microsoft broadened its warning, saying connectivity issues could affect users in any region.
Through Thursday evening and overnight, Microsoft described traffic redistribution, paused deployments and server restarts. It said a component responsible for processing server health might be causing automated checks to fail. At 22:09 UTC, the company said a core process on affected servers was becoming overwhelmed; a later service-health update described a process involved in establishing secure connections becoming overloaded and preventing servers from processing requests.
Microsoft also said it had begun reverting a recent network configuration change that correlated with the start of the impact, but later reported that a change it had applied was not working as expected. The company said it had no indication of malicious activity. A separate Teams incident, TM1550488, was marked fully resolved at 17:09 UTC Thursday; BleepingComputer reported that Microsoft had not said whether it was connected to EX1550543.
“Servers are stable where a patch was applied, and Microsoft is expanding the patch region by region.”
— Microsoft, in its 08:06 UTC service-health update for EX1550543
Root Cause and Full Recovery
Microsoft has not named a root cause, and its updates describe several investigation findings and remediation steps rather than a final explanation. The company said it had not identified a recent change correlated with the start of the impact, while separately noting that a network configuration change correlated with the outage and that it had begun reverting it. The available updates do not establish that this configuration change caused the incident.
It is also not clear how many users or organizations remain affected, which regions have received the patch, or when service will return to normal everywhere. Downdetector reports reflect submitted complaints, not a verified affected-user total. Microsoft has said it is not aware of malicious activity, but that statement does not explain what triggered the server failures.
The status of dependent services and third-party connectors may vary as Microsoft rolls out the patch. Microsoft has promised a Post-Incident Report after mitigation; until then, the technical cause and full scope remain unresolved.
Regional Rollout and Incident Report
Microsoft said it would continue expanding the patch region by region, beginning with areas in or entering peak business hours. Its next status updates should clarify whether stability holds as patched servers receive traffic and whether the rollout reaches the remaining affected infrastructure. Users should consult Microsoft’s service-health information for current availability rather than treating the reported improvement as a full resolution.
Once the issue is mitigated, Microsoft has said it will publish a Post-Incident Report. That report is expected to provide a fuller account of the cause and response, but Microsoft has not given a publication date in the supplied updates. Until then, the outage remains active in the status record and the timing of complete recovery is unknown.
Key Questions
Is Microsoft 365 still experiencing an outage?
Yes. As of 08:35 UTC on Nov. 13, Microsoft’s status page still listed service degradation for Microsoft 365. Microsoft reported improved stability on patched servers, but had not declared the incident resolved.
Which Microsoft 365 services are affected?
The central issue involves Exchange Online mailbox access through Outlook and REST connections. Microsoft 365 functions that depend on Exchange Online have also been reported affected, including Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner. The impact may differ by service and region.
What caused the outage?
Microsoft has not identified a confirmed root cause. Its updates describe servers becoming unavailable, an overloaded process and a configuration change it began reverting. Those details do not yet establish a final cause.
Was the outage caused by a cyberattack?
Microsoft said it had no indication of malicious activity. The company has not provided a final technical explanation, and it has promised a post-incident report after mitigation.
When will Microsoft 365 be fully restored?
Microsoft has not provided a full-recovery estimate. It said it was expanding a patch region by region after seeing stable servers where the patch had been applied, but the service remained degraded in its latest supplied status.
Source: ThorstenMeyerAI.com
