For most of the U.S. working day on Thursday, many people could not open Outlook, Teams messages could not be sent, and Copilot did not respond.
The outage began just before 1 p.m. The number of reports on Downdetector peaked at about 200,000 at around 1 p.m. New York time, including nearly 140,000 for Outlook alone. Microsoft initially said that the infrastructure load in multiple regions was too high, but later confirmed that some servers were unexpectedly unavailable, and the pressure was transferred to the remaining servers, crushing them.
In an update at around 5 p.m., Microsoft said the measures it had taken "have not yet achieved the desired results." The problem was that a core process on the affected server was overloaded, causing the server to stop responding. Limited recovery was seen in some areas only after 6 p.m.
The impact is not just on office software. A listed company cited a Microsoft glitch as an excuse to postpone its financial report scheduled to be released on that day to next Monday; school districts, universities, and hospitals all issued reminders of restricted communications. Anthropic and OpenAI also reported outages of their own services during the same period.
Copilot was dragged into the water this time, indicating that the AI assistant has been deeply bound to underlying services such as Exchange and OneDrive. If the mail cannot come in, the AI will have nothing to read; if the file cannot be opened, the AI cannot write a summary.
For teams that have all their work processes on a cloud, this is a reminder: leave at least one backup communication channel, and keep a copy of key documents locally.