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TL;DR
Microsoft 365 remained degraded at 08:35 UTC on Nov. 13, after Exchange Online problems that began Thursday disrupted email and connected services. Microsoft reported improved server stability following a patch and is expanding it region by region, but has not identified the root cause.
Microsoft 365 remained in service degradation as of 08:35 UTC Friday, Nov. 13, after Exchange Online access problems disrupted email and connected services from Thursday. Microsoft said a patch had produced positive results for server stability and that it was expanding the fix region by region; the company has not disclosed the root cause.
The incident is tracked as EX1550543. Microsoft’s status updates say many users have been unable to reach Exchange Online mailboxes through Outlook on the web, desktop and mobile, as well as through REST connections. The disruption also affected services that rely on Exchange Online, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s explanation evolved as it investigated. It first described elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. The company paused deployments, redirected traffic, restarted affected servers and changed its server health-check method. It later said a core process on affected servers was becoming overwhelmed; returned servers could become unresponsive again when traffic resumed.
At 07:29 UTC Friday, Microsoft reported improved stability after applying a patch to part of its infrastructure. In an 08:06 UTC update to the Exchange Online record, it said it had begun expanding the patch systematically, starting with regions in or entering peak business hours. Microsoft’s status page still listed the service as degraded at 08:35 UTC, so the update did not confirm a full recovery.
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 Beyond Email
The outage matters because Exchange Online supports more than mailbox access: problems with it can affect scheduling, collaboration and other Microsoft 365 tools used together in workplaces. A service may appear available while functions that depend on Exchange Online remain impaired, making it harder for teams to coordinate meetings or use connected workflows.
The effects also reached organizations and third-party services. OpenAI and Anthropic reported errors with their Microsoft 365 connectors, according to the source material. Workhorse Group moved its third-quarter earnings call from Nov. 12 to Nov. 16 because of the outage. These examples show operational consequences, but do not establish that every customer or integration was affected.
Reports collected by Downdetector indicated widespread complaints, including more than 130,000 Outlook problem reports in the United States at the reported peak around 1 p.m. ET Thursday. Such reports are user-submitted reports, not a count of affected people; they indicate the scale of complaints, not how many users lost access.
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From Thursday Reports to Friday Patch
Microsoft’s first public notice came at 17:54 UTC Thursday, when its Microsoft 365 Status account said it was investigating reports of Exchange Online mailbox access problems in the Americas. A copy of the service-health post on Cloud Admin Hub places the incident start at 16:17 UTC. At 18:07 UTC, Microsoft said the issue might affect connectivity in any region.
Through Thursday evening and overnight, Microsoft described efforts to redistribute traffic, pause deployments and restart servers. The company later said restarts had not provided lasting relief and that a secure-connection process on affected servers was becoming overwhelmed. At 01:06 UTC Friday, it also said it had begun reverting a recent network configuration change that correlated with the start of the impact. It subsequently reported that one change was not working as expected, before announcing better stability after a patch at 07:29 UTC.
A separate Teams incident, tracked as TM1550488, was marked fully resolved at 17:09 UTC Thursday. BleepingComputer reported that Microsoft had not said whether that incident was related to EX1550543. The source material also cites reports of complaints across 74 countries; because those figures come from Downdetector reporting, they should not be read as verified counts of affected users.
“We have initiated its expansion systematically.”
— Microsoft, Exchange Online service-health update at 08:06 UTC, Nov. 13
Root Cause and Recovery Remain Unknown
Microsoft has not named a root cause or confirmed that the patch will restore service across all regions. Its updates describe server unavailability, overwhelmed processes and a network configuration change that correlated with the incident’s start, but those details do not amount to a final explanation of what triggered the failure.
The company said it was not aware of malicious activity. That is a statement about its investigation at the time, not a published post-incident finding. It has promised a Post-Incident Report once the problem is mitigated. Until then, the full scope, the duration of remaining disruption and whether all affected Microsoft 365 services will recover together remain unclear.
The status page still showed service degradation at 08:35 UTC Friday. Microsoft had not given a completion time in the supplied updates, and there was no confirmation that every affected customer or region had regained normal access.
Watch Regional Patch Expansion
Microsoft said it was expanding the patch region by region, prioritizing areas in or entering peak business hours. Customers should monitor Microsoft 365 service health and the EX1550543 record for changes to the incident status, affected services and recovery guidance. A reported improvement in stability is not the same as a confirmed resolution.
Organizations can use their established internal continuity procedures while access remains unreliable, such as communicating through an approved alternative channel and postponing time-sensitive work that depends on affected services where practical. Users should follow their IT department’s instructions and avoid treating unverified third-party outage reports as a measure of their organization’s own service status.
Microsoft’s next key milestone is confirmation that the regional expansion has restored affected services and that the incident can be mitigated. The company has said it will publish a Post-Incident Report afterward; that report is expected to provide more detail on cause and remediation, though no publication time was given in the supplied material.
Key Questions
Is the Microsoft 365 outage over?
No. Microsoft’s status page still listed service degradation at 08:35 UTC on Nov. 13. The company reported improved server stability and was expanding a patch, but had not declared the incident resolved.
Which services have been affected?
Microsoft reported problems accessing Exchange Online mailboxes through Outlook on the web, desktop, mobile and REST connections. The source material also lists effects on Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Defender XDR, Purview and Planner.
What should users do while services are disrupted?
Check the Microsoft 365 service-health page or ask your organization’s IT team for status and instructions. Follow approved continuity procedures for time-sensitive work; Microsoft had not provided a confirmed recovery time in the updates supplied here.
Has Microsoft identified the cause?
No. Microsoft described unavailable servers and an overwhelmed process involved in establishing secure connections, and said a network configuration change correlated with the start of the impact. It has not published a root cause and said it would issue a Post-Incident Report after mitigation.
Does the outage appear to be a cyberattack?
Microsoft said it was not aware of malicious activity. That is the company’s current statement, not a final public account of the cause; the investigation and outage were still ongoing in the latest supplied update.
Source: ThorstenMeyerAI.com
