If you were having trouble accessing certain services like Microsoft Teams or Outlook, you were not alone. Early Thursday afternoon, many of Microsoft's biggest apps and services were experiencing downtime. According to Downdetector, which tracks user reports of issues with websites and platforms, Microsoft 365, Teams, Copilot, Teams, and OneDrive were all experiencing issues. As of Friday afternoon, Microsoft has restored service to many users, and has officially apologized for the outages. Which Microsoft services were affected by the outages?When I first published this article on Thursday, I couldn't even load Microsoft 365's status page. (I've reported on many service outages, but I can't recall a time when a service's status page was also down.) Even as of Friday afternoon, the page still says "Service degradation on Microsoft 365 (Business or Enterprise)," and Microsoft says the following services may be affected: Exchange Online, Microsoft 365 admin center, Microsoft 365 apps, Microsoft 365 Apps Admin Center, Microsoft 365 Education, Microsoft Copilot 365, Microsoft Defender for Office 365, Microsoft Defender XDR, Microsoft Fabric, Microsoft Graph, Microsoft Intune, Microsoft Planner, Microsoft Power Apps, Microsoft Purview, Microsoft Teams, Microsoft To Do, Power BI, SharePoint Online, Universal Print, and Windows 365. Looking specifically at Outlook, Microsoft's email service had hundreds of thousands of user reports Thursday afternoon, signaling a major issue somewhere in Microsoft's pipeline. The reports did "slow down" throughout the day, but Downdetector still showed over 50,000 reports coming in every 15 minutes when I checked Thursday afternoon. What caused these Microsoft outages?While the root cause of the issue was a mystery throughout Thursday's outage, Microsoft confirmed the problem in an apology on Friday. According to the company, "This was a technical issue not related to cyber or AI [or] agents. The incident was introduced by an issue during an earlier network capacity upgrade that surfaced following a recent network change. We have addressed the underlying issue and continue to restore service to remaining customers and regions." Microsoft says it is "deeply sorry" for the disruption to its customers and partners. The company says the fix rolled out slower than some might expect, since it wanted to restore service gradually to evaluate stability at each stage. It also says it will release a full post-incident report once it completes a review.During the outage, the company had confirmed that some of its infrastructure was experiencing elevated load, which it said was likely contributing to the issues. Microsoft then said it was pausing all deployments and moving traffic from affected infrastructure, and that it found that a number of its servers were unexpectedly unavailable after failing health checks. The company then thought a specific component responsible for processing server health may be the reason the system is failing health checks. Microsoft said an alternative service health check method successfully restarted some of the affected servers. The company was then actively restarting and validating affected servers to bring them back to service. This Tweet is currently unavailable. It might be loading or has been removed.