🔍 Read the full analysis: Microsoft 365 Outage: What Broke, Microsoft’s Response, And Next Steps on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained degraded as of 08:35 UTC on November 13, after Exchange Online problems disrupted email and connected services from November 12. Microsoft reported improved stability on servers that received a patch and said it was expanding the patch region by region; it has not identified the root cause.
Microsoft 365 remained degraded as of 08:35 UTC Friday, November 13, after an outage that began the previous day disrupted Exchange Online and services that rely on it. Microsoft said a patch had improved stability on some servers and that it was expanding the patch region by region, but the company had not named a root cause and had not declared the incident resolved.
The main reported problem is access to Exchange Online mailboxes. Since Thursday, users have experienced problems connecting through Outlook on the web, desktop and mobile apps, as well as REST connections. The disruption has also affected functions that depend on Exchange, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner.
Microsoft’s account of the issue changed as its investigation progressed. It first described elevated load across multiple regions, then said the load was not caused by increased traffic but by servers becoming unexpectedly unavailable. Microsoft paused deployments, moved traffic, restarted affected servers and changed its method for checking server health. It later reported that a core process on affected servers was becoming overwhelmed, leaving them unable to handle requests.
Restarts did not provide a lasting fix: Microsoft said some returned servers became unresponsive again after receiving traffic. At 07:29 UTC Friday, it reported positive stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. In its 08:06 UTC update for incident EX1550543, Microsoft said servers were stable where the patch had been applied and that expansion was underway, starting with regions in or entering peak business hours.
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 the outage reached other services
The disruption matters beyond email because Exchange Online supports connected Microsoft 365 functions. When users cannot reach mailboxes, calendar access and meeting scheduling can also be impaired, while other services may experience knock-on effects. That can interrupt routine work for organizations that use Microsoft’s cloud tools for communications, documents, scheduling and security administration.
There were reported effects beyond Microsoft’s own products. The source report said OpenAI and Anthropic reported errors with their Microsoft 365 connectors. Workhorse Group also moved its third-quarter earnings call from November 12 to November 16 because of the outage, according to the report. These examples show how a cloud-service disruption can affect integrations and business plans, although the available information does not establish the full scale of those impacts.
Reports on outage-tracking services give 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 Outlook problem reports in the United States at the peak, around 1 p.m. ET Thursday. Business Standard, citing Downdetector, reported complaints from 74 countries. Those figures should not be read as confirmed counts of affected users.
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How Microsoft’s diagnosis changed
Microsoft’s first public notice appeared at 17:54 UTC Thursday, saying it was investigating reports of users unable to access Exchange Online mailboxes through multiple connection methods in the Americas. The service health record gives the incident start time as 16:17 UTC. At 18:07 UTC, Microsoft broadened its warning, saying connectivity problems could affect users in any region.
During Thursday evening and overnight, the company reported attempts to redistribute traffic and restart servers, followed by changes to server health checks. It later said a process responsible for establishing secure connections was becoming overwhelmed. Microsoft also said it had begun reverting a recent network configuration change that correlated with the start of the incident, but an attempted change was not working as expected. The sequence reflects the company’s evolving investigation; it does not establish a confirmed root cause.
A separate Teams issue, tracked as TM1550488, was marked fully resolved at 17:09 UTC Thursday. The source report, citing BleepingComputer, said Microsoft had not stated whether that incident was connected to the Exchange Online outage. Microsoft’s 04:10 UTC Friday update said there was no indication the outage resulted from malicious activity.
“The elevated load isn’t driven by an increase in traffic, but by a number of servers being unexpectedly unavailable.”
— Microsoft, in its November 12 service updates
Root cause and recovery remain unknown
Microsoft has not identified a root cause or said when the outage will be fully resolved. Its updates describe unavailable servers, failed health checks and an overwhelmed process, and mention a network configuration change that correlated with the incident’s start. The company has not confirmed that this configuration change caused the outage.
It is also not clear how many customers or regions remained affected at 08:35 UTC, how quickly the patch would reach all relevant infrastructure, or whether services would remain stable as traffic returned. Downdetector reports measure submissions by users, not independently verified outages or affected people. Microsoft has said it will publish a Post-Incident Report after mitigation; its findings are not yet available.
Microsoft’s regional patch rollout
Microsoft said it was expanding the patch region by region, prioritizing areas in or approaching peak business hours. Its next reported milestone is whether stability holds as patched servers receive normal traffic and whether the rollout restores access across Exchange Online and dependent services. The outage should be treated as ongoing until Microsoft changes the service status and confirms recovery.
Microsoft has promised a Post-Incident Report once the issue is mitigated. That report is expected to provide further detail on the cause, the response and the impact, but no publication time was given in the source material. Until then, customers and administrators can follow Microsoft’s service health updates for incident EX1550543; the information available does not establish a complete recovery timetable.
Key Questions
Is Microsoft 365 back up?
Not according to the status reported here. At 08:35 UTC on November 13, Microsoft still listed service degradation. The company reported stable servers where its patch had been applied, but was still expanding the rollout.
Which Microsoft 365 services were affected?
The main issue involved Exchange Online mailbox access through Outlook and REST connections. The source report also listed impacts to Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, Microsoft Defender XDR, Purview and Planner.
What caused the outage?
The root cause has not been confirmed. Microsoft described unexpectedly unavailable servers and an overwhelmed process, and said a network configuration change correlated with the start of the impact. It has not said that this was the confirmed cause.
Was the outage caused by a cyberattack?
Microsoft said in a 04:10 UTC update that it had no indication of malicious activity. That is the company’s reported assessment; its investigation and final incident report were still pending.
When will Microsoft publish more information?
Microsoft said it would publish a Post-Incident Report after mitigation. The source material gives no publication date or confirmed time for full service restoration.
Source: ThorstenMeyerAI.com
