Microsoft 365 users across multiple regions experienced connectivity errors Thursday as the tech giant worked to resolve a widespread hours-long outage caused by elevated system loads.

As of early Friday, the disruption remained unresolved in the United States and had extended into the workday across the Asia-Pacific region, as Microsoft continued working to restore service.

The “elevated load” wasn’t driven by an increase in traffic, according to an alert from the Microsoft Admin Center. Instead, it was the result of a “number of servers being unexpectedly unavailable, straining the remaining infrastructure.”

“We’re working to safely return them to service,” Microsoft said, adding it was “aggressively pursuing all pathways to reduce impact.”

By 6:30 p.m. ET, the company said it was opening all available pathways to restore service, “as our actions taken thus far have not provided the anticipated relief.”

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A widespread Microsoft Outlook outage was reported by users Thursday.  (Toby Scott/SOPA Images/LightRocket via Getty Images / Getty Images)

“We found a core process on affected servers is becoming overwhelmed, causing capacity loss,” Microsoft wrote in a statement. “To validate a potential recovery, we’re isolating a portion of infrastructure, restarting affected components, and reintroducing traffic to confirm the services remain stable before applying the change more broadly.”

“The servers we returned to service can become unresponsive again once they receive traffic; we’re analyzing diagnostic data to determine what’s triggering the behavior,” another alert stated. “In parallel, we’re temporarily limiting which types of traffic can reach the affected infrastructure in some locations. Additionally, we’re rebuilding a subset of affected servers using a previous configuration to validate if this prevents them from becoming unresponsive.”

The outage has potentially impacted thousands of users trying to access their emails through Microsoft 365.

In an 8:59 p.m. ET update, Microsoft reported progress in restoring service, saying efforts to restart affected infrastructure and recover server availability were producing positive results. The company said it was monitoring the affected systems to verify their stability before expanding recovery efforts more broadly, which it expects could improve service availability.

In a subsequent update at 10:13 p.m. ET, Microsoft said its efforts to improve service availability were not producing the expected results.

“We’re identifying alternate workstreams that can be applied to increase capacity in the face of sustained traffic management imbalances,” Microsoft wrote on X.

At 11:36 p.m. ET, Microsoft reported “partial service recovery” in some regions but said the improvements had not been sustained.

Other impacted services include:

• Exchange Online: Users may be unable to access their mailbox using Outlook on the web, Outlook desktop (MAPI), Exchange ActiveSync (EAS), or REST-based connections, and email delivery may be delayed.
• Microsoft 365 admin center: Admins may be unable to load some admin center pages.
• Microsoft 365 apps: Users may be unable to view their recently used files.
• Microsoft 365 Apps Admin Center: Multiple services including Cloud Update, Cloud Policy and Inventory are affected.
• Microsoft 365 Education: Features including Assignments, Reading Progress, and Speaker Progress may be impacted.
• Microsoft Copilot 365: Users may be unable to load Copilot Chat or receive responses in the web and desktop apps, and Copilot experiences may be unable to access work data such as email, calendar and files.
• Microsoft Defender for Office 365: Safe Links may be unable to verify URLs, which may impact users clicking links in Outlook and Teams.
• Microsoft Defender XDR: Users may be unable to load Microsoft Defender portal pages or solution tabs.
• Microsoft Fabric: Users may encounter failures when exporting reports with sensitivity labels to PDF or PowerPoint, or when updating artifacts with sensitivity labels.
• Microsoft Graph: API requests that access Exchange Online data — such as mail, calendar and contacts — may time out.
• Microsoft Intune
• Microsoft Planner: Users are experiencing Plan and Task operation reliability issues.
• Microsoft Purview: Multiple Purview services including Authorization, auto-labeling, Data Loss Prevention (DLP), Communication Compliance, and Data Classification are impacted, and users may be unable to load Microsoft Purview portal pages.
• Microsoft Teams: Scenarios that depend on Exchange Online — including calendar, meeting scheduling, and creating chats for organizations using Information Barriers — may fail. Core messaging and online meetings remain largely functional.
• Microsoft To Do: The app may not load, and users may see operation failures.
• Power BI: All users may intermittently be unable to export reports with MIP sensitivity labels to PDF in Power BI.
• SharePoint Online: Features that depend on Exchange Online may be impacted. Accessing files stored directly in SharePoint Online remains functional.
• Universal Print: Users may encounter errors submitting print jobs or using admin features.
• Windows 365: Customers who have configured their tenant and Cloud PCs to use Microsoft Purview Customer Key for Windows 365 Cloud PCs may have users who are unable to connect to their Cloud PCs.

Microsoft said it is continuing work to “isolate the issue affecting server availability, as well as other workstreams.”

The logo of productivity software Microsoft 365 is displayed on a smartphone in front of abstract background on computer screen.  (Getty Images / Getty Images)

Cybersecurity expert Leeza Garber told FOX Business that Microsoft is dealing with an “increased load,” meaning: “There’s so much happening on a lesser amount of servers, not because there’s more people using it because there’s more traffic, but simply because there’s less servers available.”

“This kind of problem is actually pretty simplistic, but on the scale at which Microsoft is operating, it can shut everything down,” Garber added. “We’ve seen outages like this before, hitting Amazon, hitting Google, over the past decade, some being extremely large scale around the globe.”

In an earlier update posted to its official channels, Microsoft said that engineers had pinpointed the source of the disruption, noting that a portion of its infrastructure was experiencing heightened traffic and strain.

An investigation indicated that failed health checks may have originated from an unidentified component responsible for processing server health, the company said. Steps were taken to prevent additional servers from being impacted.

Data collected by Downdetector, a website that tracks issues with websites and software, showed more than 130,000 problems have been reported, as of 2 p.m. Thursday.

Downdetector also reported user issues with Xbox and Amazon, but it was not immediately clear how widespread the problems were. 

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Microsoft 365 has roughly 321 million users globally, according to Dynamics Connect. It was unclear Thursday how long the outage might last or how it could impact the workforce.

Portland Fire & Rescue in Oregon said that anyone sending an email to agency employees may experience delayed replies. Emergency crews were still being dispatched for calls, the agency said. 

The White House did not immediately respond to FOX Business’ request for comment.