Microsoft 365 and Outlook Outage Hits Thousands of US Users on Thursday

Microsoft 365, Outlook and Teams went down for thousands of users in the United States on Thursday, November 12, in an outage that also broke connectors used by the OpenAI and Anthropic AI services. The tracking site Downdetector logged the first sharp rise in reports just after 12:00 p.m. ET, and the numbers climbed for more than an hour before they started to fall.

Outlook took the worst of it. USA Today, citing Downdetector, reported that Outlook problems had reached just shy of 83,000 reports just before 1:00 p.m. ET and peaked at 128,874 reports at 1:09 p.m. ET. By about 1:50 p.m. ET the Outlook count had dropped to 92,914. Reuters, also citing Downdetector, put Outlook at more than 97,000 reports at 2:07 p.m. ET, with more than 38,000 reports for Microsoft 365 and about 4,500 for Teams at the same time. The counts are snapshots taken at different times, so they do not add up to one total.

Microsoft points to servers that went unavailable

Microsoft said it was investigating reports of users having trouble reaching Exchange Online mailboxes through multiple connection methods in the Americas. The company tracked the problem in the Microsoft 365 admin center under incident EX1550543, and it later said the issue may affect Microsoft 365 service connectivity for users in any region.

In an update at 18:43 UTC, Microsoft described a pattern in which affected servers become intermittently unavailable, which puts extra strain on the servers still working and adds to the connection problems. The Detroit Free Press reported a later Microsoft statement that said the same thing in plainer terms: "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."

Microsoft told users it was moving traffic and restarting servers. "We're aggressively pursuing all pathways to reduce impact. We've paused all deployments, we're moving additional traffic off the affected infrastructure, and we're restarting affected servers to return them to service," the company said in an update reported by USA Today. It also warned that shifting Outlook connection traffic to balance the load could cause latency for some users.

AI tools and an earlier Teams problem

The outage reached past email. Reuters reported that OpenAI said it was investigating an issue with Microsoft connectors in which new connections may be broken and tools are not working as expected. Anthropic said it had found an issue with an upstream provider that affected its Microsoft 365 connector.

The afternoon failure was the second Microsoft disruption of the day. Earlier on Thursday, Reuters reported, Microsoft said it had fixed a separate Teams disruption that affected users in North America and that its impact had been fully resolved. Microsoft had not, in the reports cited here, given a time for a full fix for the Outlook and Microsoft 365 outage.