🔍 Read the full analysis: Day Two Of The Microsoft 365 Outage: What’s Broken And What’s Next on ThorstenMeyerAI.com
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TL;DR
Microsoft 365 remained degraded as of 08:35 UTC on Nov. 13, after users began reporting Exchange Online access problems the previous day. Microsoft says a patch has improved stability on part of its infrastructure and is being expanded region by region; the cause is still unknown.
Microsoft 365 remained degraded on Friday morning, Nov. 13, as Microsoft expanded a patch intended to stabilize servers affected by an outage that began the previous day. In its 08:06 UTC update for Exchange Online incident EX1550543, Microsoft said servers were stable where the patch had been applied and that it was rolling it out region by region; the company had not identified a root cause.
The disruption affects access to Exchange Online mailboxes through Outlook on the web, desktop and mobile apps, as well as REST connections, according to the incident information summarized by ThorstenMeyerAI.com. Services that depend on Exchange Online have also experienced effects, including Teams calendars and meeting scheduling, parts of SharePoint Online, Microsoft 365 Copilot, the Microsoft Defender XDR portal, Purview and Planner. The exact degree of impact can vary by service and user.
Microsoft’s updates describe a changing diagnosis. It first pointed to elevated load across multiple regions, then said that load was not caused by increased traffic but by servers becoming unexpectedly unavailable, placing pressure on the remaining infrastructure. The company paused deployments, redirected traffic, restarted affected servers and changed its server health-check approach. It later reported that a core process on affected machines was becoming overwhelmed, and that servers returned to service could become unresponsive again when they received traffic.
On Friday, Microsoft reported positive server-stability results after applying an upstream authentication and routing configuration component patch to part of its infrastructure. The 08:06 UTC update said expansion was proceeding systematically, beginning with regions in or entering peak business hours. Microsoft’s status page still showed “Service degradation” at 08:35 UTC, so the improvement did not mean the outage was resolved.
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 Reaches Other Tools
The disruption extends beyond inbox access because Exchange Online supports connected Microsoft 365 functions. Problems with mailboxes can interfere with calendars and meeting scheduling, while other listed services may have trouble when they rely on affected infrastructure. For organizations using Microsoft 365 for daily communications and coordination, even partial or regional instability can interrupt routine work.
The effects have also reached services and businesses outside Microsoft’s own product suite. ThorstenMeyerAI.com reported that OpenAI and Anthropic flagged errors with their Microsoft 365 connectors. 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 possible downstream consequences, but they do not establish that every user of those services was affected.
Numbers cited from outage trackers also need careful interpretation. Reuters, in a report published by The Korea Times, said Downdetector recorded more than 130,000 U.S. Outlook problem reports near a peak around 1 p.m. ET Thursday. Business Standard cited reports from 74 countries. Downdetector counts submissions from users, not verified affected people, so those figures indicate complaint volume rather than the number of customers unable to work.
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From Thursday Reports to Friday Patch
The first public notice described in the source appeared at 17:54 UTC on Thursday, Nov. 12, when Microsoft’s 365 Status account said it was investigating Exchange Online mailbox access problems in the Americas. A service-health record cited by Cloud Admin Hub lists the incident start as 16:17 UTC. At 18:07 UTC, Microsoft said the issue could affect Microsoft 365 connectivity in any region.
Microsoft’s overnight updates outlined a sequence of attempted responses: traffic redistribution, a pause on deployments, server restarts and an alternative health-check method. The company later said the restarts had not provided the expected relief, reporting that affected servers could fail again under traffic. At 01:06 UTC Friday, Microsoft said a process responsible for establishing secure connections was becoming overwhelmed and that it had begun reverting a recent network configuration change correlated with the start of the impact.
A separate Teams incident, TM1550488, was marked fully resolved by Microsoft at 17:09 UTC Thursday, according to the source. BleepingComputer reported that Microsoft had not said whether that incident was related to the ongoing Exchange Online disruption. The available updates do not establish a connection between the two.
““We’ve initiated its expansion systematically,” starting with regions in or entering peak business hours.”
— Microsoft, in its 08:06 UTC Nov. 13 Exchange Online service-health update
Root Cause and Full Recovery Remain Unknown
Microsoft has not named the root cause, and its updates have described multiple possible contributing mechanisms, including failed health checks, an overwhelmed server process and a network configuration change that correlated with the start of the impact. Correlation does not establish that the configuration change caused the outage. The source material also reports that Microsoft said it had found no recent change correlated with the start at one stage of its investigation.
It is not yet clear how quickly the patch will reach all affected regions, whether stability will hold as more traffic returns, or when Microsoft 365 will be fully restored. Microsoft’s status page continued to list service degradation as of 08:35 UTC. The reported tracker totals are user reports rather than verified counts of affected customers, and the relationship, if any, between the separate Teams incident and EX1550543 has not been stated.
Microsoft’s Regional Rollout and Incident Report
Microsoft said it was expanding the patch region by region, prioritizing areas in or approaching peak business hours. Users and administrators should treat the incident as ongoing until Microsoft updates the service-health record and confirms recovery; the available information does not provide a firm restoration time.
Microsoft has said it plans to publish a Post-Incident Report after the problem is mitigated. That report is expected to provide more information about the cause and response, though its publication timing was not specified in the source material. Until then, the key milestones to watch are whether the patch remains effective as traffic returns and whether Microsoft changes the service status from degradation.
Key Questions
Is the Microsoft 365 outage over?
No. Microsoft’s status page still listed service degradation as of 08:35 UTC on Nov. 13. The company reported stability improvements on patched infrastructure but was still expanding the patch.
Which services are affected?
The reported disruption centers on Exchange Online mailbox access through Outlook and REST connections. Reported knock-on effects include Teams calendars and meeting scheduling, parts of SharePoint Online, Copilot, the Defender XDR portal, Purview and Planner; the extent may vary.
What caused the outage?
Microsoft has not identified or announced a root cause. Its updates have described unavailable servers, overwhelmed processes and a network configuration change correlated with the start of the impact, but the available information does not establish a definitive cause.
Is Microsoft investigating a cyberattack?
Microsoft said it was not aware of any malicious activity. That is the company’s reported assessment; it has not yet issued the promised post-incident report.
When will service return to normal?
No restoration time has been announced in the available updates. Microsoft said it was expanding the patch region by region and would publish a Post-Incident Report after mitigation.
Source: ThorstenMeyerAI.com
