{"id":4214,"date":"2026-11-12T14:46:13","date_gmt":"2026-11-12T22:46:13","guid":{"rendered":"https:\/\/cyber.mag212.com\/microsoft-365-outage-outlook-teams-exchange-online-12-november-2026\/"},"modified":"2026-11-12T14:46:13","modified_gmt":"2026-11-12T22:46:13","slug":"microsoft-365-outage-outlook-teams-exchange-online-12-november-2026","status":"publish","type":"post","link":"https:\/\/cyber.mag212.com\/fr\/microsoft-365-outage-outlook-teams-exchange-online-12-november-2026\/","title":{"rendered":"Microsoft 365 Outage: Outlook, Teams and Exchange Online Down as Servers Fail Health Checks"},"content":{"rendered":"\n

If Outlook stopped loading this afternoon, it wasn\u2019t your computer, your password or your network. A large Microsoft 365 outage on Thursday, 12 November 2026 left users across the Americas and beyond unable to reach their mailboxes, and spread to Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR. Microsoft says the cause is a set of its own servers failing automated health checks, and so far there is no evidence of a cyberattack. Here is what happened, what Microsoft has said, and what users, IT teams and MSPs should do while service comes back.<\/p>\n\n\n\n

What<\/strong><\/td>Microsoft 365 connectivity outage centred on Exchange Online (business Outlook)<\/td><\/tr>
When<\/strong><\/td>Thursday 12 November 2026; incident opened 16:17 UTC (8:17 a.m. PT), still listed as degraded at 22:11 UTC (2:11 p.m. PT)<\/td><\/tr>
Services named by Microsoft<\/strong><\/td>Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot, Defender XDR; later Planner, To Do and Purview services<\/td><\/tr>
Cause (per Microsoft)<\/strong><\/td>Servers failing automated health checks and becoming unavailable, straining the rest of the service<\/td><\/tr>
Attack?<\/strong><\/td>No evidence disclosed<\/td><\/tr>
Tracking IDs<\/strong><\/td>EX1550543 and MO1550821 in the Microsoft 365 admin center<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

What happened<\/h2>\n\n\n\n

[Confirmed]<\/strong> Microsoft\u2019s service health record, mirrored by the University of Wisconsin\u2013Milwaukee, shows an Exchange Online incident starting at 10:17 a.m. Central (16:17 UTC): users \u201cmay be unable to connect to their mailboxes in Exchange Online through multiple connection methods.\u201d By 11:45 a.m. Central Microsoft had found connectivity errors on the part of Exchange Online that receives and processes users\u2019 access requests, and by 12:29 p.m. it had moved some US traffic away from the affected infrastructure. (UWM, quoting Microsoft<\/a>)<\/p>\n\n\n\n

[Reported]<\/strong> Public reports surged around 12:40 p.m. Eastern. Downdetector logged a peak of roughly 130,000 Outlook problem reports, with Chicago, Seattle and New York among the hot spots. (NBC Chicago<\/a>) (CNBC<\/a>) At 1:26 p.m. Eastern Microsoft opened a wider incident, MO1550821, warning that customers might be unable to connect to Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR. (BleepingComputer<\/a>) A separate Teams problem earlier in the day had already been fixed at 17:09 UTC. (Technobezz<\/a>)<\/p>\n\n\n\n

\"Timeline
Key moments in the outage, in UTC (subtract eight hours for Pacific time). Diagram: MAG212 CYBER<\/figcaption><\/figure>\n\n\n\n

What caused it<\/h2>\n\n\n\n

[Confirmed by Microsoft, via press]<\/strong> Microsoft first blamed \u201celevated load\u201d on part of its infrastructure, then corrected itself: the load was not driven by more traffic, but by a number of servers being unexpectedly unavailable and straining the rest. (ABC News<\/a>) Shortly before 3 p.m. Eastern it said the affected servers were failing automated health checks, that it was testing a workaround that bypasses the component processing those checks, and that it was looking into elevated processor usage on the affected machines. (SecurityWeek<\/a>)<\/p>\n\n\n\n

[Reported]<\/strong> Microsoft then said it had stopped more servers from being affected, began returning a subset to service around 4 p.m. Eastern, and successfully tested an alternative way of checking server health on part of the fleet. It is preparing an automated process to find and restart servers that stop responding. (Forbes<\/a>) (Mitchell Now<\/a>) At 22:11 UTC the service health page still listed a service degradation, with the next update due at 23:30 UTC. (Technobezz<\/a>)<\/p>\n\n\n\n

Was it a cyberattack?<\/h2>\n\n\n\n

[Reported]<\/strong> Microsoft has disclosed no evidence of an attack. The outage came two days after November\u2019s Patch Tuesday, which included an exploited Outlook flaw (CVE-2026-124194), but Microsoft\u2019s advisories have not linked that vulnerability to the outage. (SecurityWeek<\/a>) [MAG212 analysis]<\/strong> Everything Microsoft has described so far, servers failing health checks, high processor use and a staged restart, fits an internal reliability failure. We\u2019ll update this article if that changes.<\/p>\n\n\n\n

Who is affected<\/h2>\n\n\n\n