Major Microsoft services, including Outlook, Teams, and Microsoft 365, experienced widespread outages affecting thousands of U.S. users on Thursday.

The disruption also extended to integration connectors used by AI providers OpenAI and Anthropic.

Almost 130,000 users reported problems accessing Outlook just after 1 p.m. ET on outage tracker Downdetector, a website that tracks outages by aggregating status reports from several sources.

Reports have since fallen some but many users said they still couldn’t send and receive emails or had trouble loading their inboxes altogether.

Downdetector also recorded more than 38,000 user reports concerning problems with Microsoft 365, alongside roughly 4,500 reports of users encountering difficulties accessing Teams.

“We’re aggressively pursuing all pathways to reduce impact,” Microsoft said in a statement.

The company said that its team paused all deployments and was routing additional traffic away from the affected infrastructure while restarting impacted servers to bring them back into service.

In an update at 1:35 p.m., Microsoft said it determined “a portion of infrastructure is experiencing elevated load across multiple regions, which is likely contributing to the connectivity errors.”

“We determined the elevated load isn’t driven by an increase in traffic, but by a number of servers being unexpectedly unavailable; straining the remaining infrastructure. We’re working to safely return them to service,” the company wrote in a follow-up post.

Another update at 2:50 p.m. read, “We’re testing a configuration change to address a problem that’s causing servers to fail automated health checks and become unavailable. In parallel, we’ve initiated a restart of all affected servers and are monitoring health as they return to service.”

“We’ve not identified any recent change correlated with the start of impact; however, our investigation indicates the failed health checks may originate from a specific component that’s responsible for processing server health. We’ve taken steps to prevent additional servers from being impacted while we work to return the affected servers to service,” the company wrote in its latest update on X.

Microsoft said earlier in the day that it had fixed a Teams disruption affecting users in North America and that the issue was fully resolved. However, the business later noted that the problem could also impact Microsoft 365 service connectivity for users in other regions.

OpenAI said it was investigating an issue involving Microsoft connectors where new connections may break and tools do not function as expected.

Anthropic said it had identified an issue with an upstream provider that was affecting its Microsoft 365 connector.