Microsoft 365 outage cause revealed

Updated on Jan. 23 at 9:43 a.m. ET: Microsoft said it had fully resolved the issues that caused a large-scale Microsoft 365 outage on Thursday, rendering a number of users unable to access their email during a workday.

"We've confirmed that impact has been resolved," Microsoft posted on X at around 1:30 a.m. ET on Friday.

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Microsoft blamed the outage on a problem processing traffic in North America, posting Thursday night that it was seeing "continued improvements in service availability and functionality as a result of our load-balancing efforts." Microsoft 365 customers can also reference the closure communication MO1221364 in their admin dashboard for more details. The communication provides a little more insight, blaming a third-party networking issue for the outage.

Microsoft 365 suffered a major outage on Thursday, leaving some users unable to send or receive emails. That's obviously not ideal in the middle of a workday.

As the afternoon bled into the evening on the East Coast, the company said it was working toward a full resolution — though folks may still see issues — and shed some light on what caused the problem.

The most recent update on Microsoft's 365 status page indicated its infrastructure either mishandled or wasn't able to handle the traffic coming its way.

Under a section labeled "root cause," the status page read, "A portion of dependent service infrastructure in the North America region isn't processing traffic as expected."

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The company also said it was "carefully rebalancing traffic across all affected infrastructure in the region." It added it was "proceeding as quickly as possible and this incremental approach will also help us identify whether any additional actions may be required to ensure longstanding recovery."

We may get further details down the line from Microsoft, but, for now, it appears the company is working toward resolving the issue.