TL;DR
Microsoft 365 remained degraded at 08:35 UTC on Nov. 13, with many users still unable to reach Exchange Online mailboxes and related services. Microsoft said a patch was stabilizing servers where applied and that it was expanding deployment region by region; it has not identified the root cause.
Microsoft said Friday that it was expanding a patch region by region after seeing improved stability on affected servers, while its status page continued to list Microsoft 365 as degraded at 08:35 UTC. The outage, which began Thursday, has disrupted Exchange Online mailbox access and affected other services that depend on it; Microsoft has not named a root cause.
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In an 08:06 UTC update to the Exchange Online incident record EX1550543, Microsoft said servers were stable where the patch had been applied. It said it had begun expanding the patch systematically, starting with regions that were at or entering peak business hours. An earlier update at 07:29 UTC reported “positive results for server stability” on a portion of its infrastructure. These updates describe progress in parts of the system, not a full recovery: Microsoft still listed the incident as a service degradation at 08:35 UTC.
The incident affects access to Exchange Online mailboxes through Outlook on the web, desktop and mobile, as well as REST connections, according to the source material. Reported knock-on effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner. OpenAI and Anthropic also reported errors with their Microsoft 365 connectors. The exact availability of each affected product may vary as Microsoft works through the incident.
Microsoft’s updates describe servers becoming unexpectedly unavailable across multiple regions. The company said the issue was not driven by higher traffic and later said a core process on affected servers was becoming overwhelmed. Restarted servers did not remain reliably available: Microsoft said some could become unresponsive again after receiving traffic. It paused deployments, redirected traffic, restarted servers and changed its server health checks before reporting improved stability after the patch.
How Mail Disruption Spreads
For organizations that rely on Microsoft 365, an Exchange Online problem can reach beyond email. Calendars, meeting scheduling and connected services may also be affected, interrupting coordination and access to work tools. Reports of errors in OpenAI and Anthropic’s Microsoft 365 connectors show that some services connected to Microsoft’s platform encountered problems as well.
The disruption has also affected a business event: Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16, citing the outage in a company announcement. That is a specific example of an operational consequence; the available source material does not establish the total financial effect on businesses or the number of people unable to work.
For users managing work during the incident, the status page and the EX1550543 record provide Microsoft’s updates on recovery. Teams and services connected to Exchange may also be affected, so users should check whether the specific function they need is available rather than assume that one working Microsoft 365 app means the broader incident is resolved. If email access is unavailable, organizations can use their established backup communication procedures and keep important drafts or deadlines recorded locally until service is restored.
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From Thursday Reports to Friday Patch
Microsoft’s first public post about the Exchange Online issue appeared at 17:54 UTC on Thursday, Nov. 12. The Microsoft 365 Status account said it was investigating reports of users having trouble accessing Exchange Online mailboxes through multiple connection methods in the Americas. A copy of Microsoft’s service health post cited by the source material lists the incident start time as 16:17 UTC.
At 18:07 UTC, Microsoft said the issue might affect Microsoft 365 connectivity in any region. At 18:35 UTC, it described elevated load across multiple regions as a likely contributor to connectivity errors. It later clarified that the load was not caused by increased traffic, but by servers becoming unexpectedly unavailable. As the incident continued, Microsoft said it had paused deployments, shifted traffic, restarted servers and revised its health checks. Overnight, it reported that some servers could become unresponsive again after they began receiving traffic.
Reports of the scale of disruption need careful interpretation. Reuters, as published by The Korea Times, reported that Downdetector recorded more than 130,000 U.S. Outlook problem reports around 1 p.m. ET Thursday. Business Standard cited reports from 74 countries. Downdetector counts submissions from users, not verified affected customers, so those figures show the volume and geographic spread of complaints; they do not establish how many people lost access.
A separate Teams incident earlier Thursday, tracked as TM1550488, was marked fully resolved by Microsoft at 17:09 UTC. BleepingComputer reported that Microsoft had not said whether it was related to EX1550543. The available information does not establish a connection between the two incidents.
““We’re investigating reports of users experiencing issues accessing Exchange Online mailboxes through multiple connection methods in the Americas.””
— Microsoft 365 Status account, 17:54 UTC on Nov. 12
Cause and Full Recovery Remain Unknown
Microsoft has not disclosed the root cause of the server failures or the overwhelmed core process. The company said it was “not aware of any malicious activity”; that is its current statement, not a public explanation of what caused the outage. Microsoft has promised a Post-Incident Report after the issue is mitigated.
As of 08:35 UTC Friday, Microsoft had not declared the incident resolved. The available updates do not give a completion time for the regional patch rollout, say how many regions or customers remained affected, or confirm when each connected service would return to normal. It is also not clear whether the earlier Teams incident was related.
Watch for Regional Recovery Updates
Microsoft’s next stated step is to keep expanding the patch region by region, prioritizing locations at or entering peak business hours. Users and administrators can follow EX1550543 and Microsoft’s service health page for changes to the incident status and affected services. The outage should be treated as ongoing until Microsoft reports that the degradation has ended and the relevant services are available.
After mitigation, Microsoft says it will publish a Post-Incident Report. That report may provide more detail on the technical cause and the sequence of events. Until then, the cause, final recovery time and full scope of the disruption remain unconfirmed.
Key Questions
Is the Microsoft 365 outage over?
No. At 08:35 UTC on Nov. 13, Microsoft’s status page still listed a service degradation. It had reported improved stability where its patch was applied and was expanding the patch region by region.
Which services have been affected?
The reported disruption includes Exchange Online mailbox access through Outlook and REST connections. Reported effects on dependent services include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner. Availability may differ by service and region.
What should I do while services are disrupted?
Check Microsoft’s service health page and incident record EX1550543 for updates on the service you need. Follow your organization’s backup communication procedures, and keep important drafts or deadlines recorded locally until access is restored.
Does Microsoft know what caused the outage?
Microsoft has not named the root cause. It said servers became unexpectedly unavailable and that a core process on affected servers was becoming overwhelmed. The company said it was not aware of malicious activity and promised a Post-Incident Report after mitigation.
Source: Thorsten Meyer AI
