TL;DR
Microsoft 365 remained degraded at 08:35 UTC on November 13, with Exchange Online mailbox access disrupted since Thursday. Microsoft says a patch is stable in treated areas and is being rolled out region by region, but it has not identified the root cause.
Microsoft’s Microsoft 365 outage continued into Friday, November 13, after disrupting access to Exchange Online mailboxes since Thursday. At 08:06 UTC, Microsoft said a patch had stabilized servers where applied and that it was expanding the fix region by region; at 08:35 UTC, its status page still listed the service as degraded.
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The incident, tracked as EX1550543, was first publicly reported at 17:54 UTC on November 12. Microsoft initially said users in the Americas were having trouble reaching Exchange Online mailboxes through multiple connection methods. At 18:07 UTC, it warned that Microsoft 365 connectivity could be affected in any region. The incident record says it began at 16:17 UTC.
Microsoft’s updates described a changing picture. The company first cited elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. It paused deployments, redistributed traffic and restarted servers. Microsoft also changed how it checked server health and later said a core process on affected servers was becoming overwhelmed. Restarts did not provide a lasting fix: returned servers could become unresponsive again once they began receiving traffic.
In an update at 07:29 UTC on Friday, Microsoft reported positive server stability results after applying a patch to part of its infrastructure. At 08:06 UTC, it said it had begun expanding the patch systematically, starting with regions in or approaching peak business hours. The status page still showed degradation at 08:35 UTC. The source material does not provide a restoration estimate.
How Mail Disruption Reached Other Tools
The outage affects work that depends on Exchange Online, not just people opening an inbox. Microsoft’s incident information lists impacts to 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 in their Microsoft 365 connectors, according to their status pages.
Those dependencies can interrupt scheduling, document access and connected services across an organization. The reported impact therefore extends beyond email, though the available information does not establish that every user or feature in each named product was affected. The duration has also had a documented business consequence: Workhorse Group moved its third-quarter earnings call from November 12 to November 16, citing the Microsoft outage.
Reports from service-monitoring sites indicate widespread complaints, but they should not be read as a count of people unable to work. Reuters, as published by The Korea Times, reported more than 130,000 Downdetector reports about Outlook in the United States near a Thursday peak around 1 p.m. ET. Business Standard reported reports from 74 countries, also citing Downdetector. These are user reports, not verified counts of affected customers.
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From Regional Alert to Global Impact
Microsoft’s first public alert focused on mailbox access in the Americas. Within 13 minutes, the company said the problem might affect connectivity in any region. CNBC reported that email and other tools were unavailable through much of the Asian business day and into the early European hours. The incident thus continued across business hours in multiple regions, while Microsoft worked on infrastructure stability and a broader patch rollout.
A separate Teams incident, tracked as TM1550488, was declared fully resolved by Microsoft at 17:09 UTC on November 12. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543. The available statements do not establish a connection between the two events.
Microsoft has said it is not aware of malicious activity and has promised a Post-Incident Report after mitigation. That statement describes the company’s current assessment; it does not identify what caused the server problems. The root cause remains unnamed in the updates available as of 08:35 UTC Friday.
““A portion of infrastructure is experiencing elevated load across multiple regions, which is likely contributing to the connectivity errors.””
— Microsoft, in its November 12 service update
Cause and Recovery Window Remain Unknown
Microsoft has not named the root cause, and it has not said when all affected services will return to normal. Its updates describe a patch that is stable in areas where it has been applied, alongside a phased expansion; they do not confirm that the patch has reached every affected region or that all dependent products are functioning normally.
The number of affected customers is also not established by the figures in the source material. Downdetector reports measure submissions from users, not confirmed outages or unique people. Microsoft’s statement that it is not aware of malicious activity is not a final account of what happened. The promised Post-Incident Report is expected to provide more detail after mitigation.
Microsoft Continues Regional Patch Rollout
Microsoft says it is expanding the patch region by region, prioritizing areas in or entering peak business hours. The next concrete indicators are further updates to service-health record EX1550543 and a change in the Microsoft 365 status page from degraded service toward recovery. Until Microsoft reports that affected services are restored, users and organizations may continue to see connectivity problems.
The company has said it will publish a Post-Incident Report once the problem is mitigated. That report should address the cause and the sequence of failures; those details are not yet available. Workhorse Group’s rescheduled earnings call is set for November 16, according to the company’s November 12 announcement.
Key Questions
Is the Microsoft 365 outage over?
No. As of 08:35 UTC on November 13, Microsoft’s status page still listed Microsoft 365 as degraded.
Which services are reported as affected?
The reported impact centers on Exchange Online mailbox access and includes Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, Defender XDR, Purview and Planner. The source does not say every user or feature is affected.
What is Microsoft doing to restore service?
Microsoft says the patch is stable on servers where it has been applied and that it is expanding the rollout region by region, with attention to regions in or approaching peak business hours.
Does Microsoft know what caused the outage?
Microsoft has not named the root cause. It has described servers becoming unexpectedly unavailable and a core process on affected servers becoming overwhelmed, and said it will publish a Post-Incident Report after mitigation.
Source: Thorsten Meyer AI
