Snow day? Microsoft on Monday confirmed a widespread, multi-hour outage affecting Outlook users, leading to email delays and failures, authentication issues, and other problems.
In a post on X, Microsoft reported the issue was impacting its Exchange Online service, its cloud-hosted platform for business email, calendar, contacts, and tasks, and then said it had identified the problem.
“We’ve confirmed that users may experience degraded functionality with various Exchange Online functionalities. We’re reviewing service telemetry and diagnostic data to isolate the source of the issue,” Microsoft wrote at 12:43 p.m. ET on Monday, after an earlier message saying it was investigating user reports of Exchange Online problems.
The company said that it identified an issue with an “authentication component” and is testing what it believes will be a remediation strategy with a portion of the infrastructure to determine if it resolves the problem. If so, it will roll out the solution more broadly. Later, it noted that the authentication component was impacting other services beyond Exchange.
We've identified an issue with an authentication component which is contributing to impact. To address this, we've developed a remediation strategy and we're applying it to a portion of infrastructure to test its efficacy. Once we've confirmed this resolves impact, we'll apply…
— Microsoft 365 Status (@MSFT365Status) August 31, 2026
We're continuing to fine-tune our remediation strategy as our internal tests progress. Additionally, we've confirmed that the authentication component issue impacts other services beyond Exchange Online. For more information regarding other impact scenarios, please see:…
— Microsoft 365 Status (@MSFT365Status) August 31, 2026
The outage is another reminder of how much of the business world today still runs on email, and particularly Outlook and Exchange.
This has been a fairly lengthy outage, as user reports started streaming in around 11:30 a.m. ET on Monday, according to the crowdsourced outage detection website Downdetector. By 2 p.m. ET, the site was seeing north of 5,000 user reports. Meanwhile, many others were complaining directly on social media platforms, like X.
Those impacted by the outage may see delays and failures in sending or receiving messages, failures when trying to search for content in their mailbox, authentication errors, failures with mailbox operations, and other workflows related to message delivery.
As of 5 PM ET on Monday, Microsoft was still trying to resolve the problem.
Our investigation indicates that a misconfiguration issue may be preventing authentication components from deploying as expected to a portion of infrastructure, and we're reexamining recent changes made to the service to determine why this is occurring. Additionally, we are…
— Microsoft 365 Status (@MSFT365Status) August 31, 2026
This article was updated after publication as Microsoft posted more information about the status of the outage.
