Problems began around 1 p.m. Eastern. Microsoft said users in the Americas were "experiencing issues accessing Exchange Online mailboxes through multiple connection methods," and that the problem may affect Microsoft 365 service connectivity for users in any region. Desktop, web and mobile versions of Outlook were all hit. Users described endless loading screens, lockouts, error codes, frozen screens and "Failed to fetch" messages. Thousands also reported trouble with Teams, Copilot and other Microsoft 365 services.

Counts of the damage vary. Downdetector user reports were put anywhere from more than 40,000 to nearly 130,000, and the differences may come down to when and where the numbers were taken. Business and enterprise customers were hit hardest, while consumer accounts were largely unaffected. Connectors for third-party AI platforms, including OpenAI and Anthropic, also broke during the outage.

Microsoft attributed the connectivity errors to "elevated load" on a portion of its infrastructure and said it was "redistributing" traffic to balance it. Its response included halting deployments, re-routing traffic and rebooting servers. A separate account of the problem traced it to how Outlook clients authenticate and connect to Exchange Online, and at one point the specific cause was not clear. Microsoft's 365 Status account confirmed the issue on X and pointed administrators to reference EX1550543 in the Microsoft 365 admin center.

At about 2 p.m., Microsoft said it was "aggressively pursuing all pathways to reduce impact." It also said it had "successfully restored" Teams in North America, though some users there still reported connectivity problems. The updates drew little patience online. One social media user called the company's wording "a very wordy way of saying 'we're down and don't know when we'll be back up.'"

Email sent during the outage is not permanently lost, according to Microsoft. Messages are held in retry queues for up to 24 hours, and a non-delivery report is generated if delivery fails. Users can check the Sent Items and Outbox folders in Outlook on the web to see where a message stands, and organizations can use the Message Trace tool, which keeps data for 90 days.