Microsoft tests fix for widespread, hours-long Outlook outage

Microsoft on Monday confirmed a widespread, multi-hour outage affecting Outlook users, causing email delays and failures, authentication issues, and other problems. In a post on X, the company said the issue was hitting Exchange Online, its cloud-hosted platform for business email, calendar, contacts, and tasks, after first saying it was investigating user reports of problems.

“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. The company later said it had identified an issue with an “authentication component” and was testing what it believed would be a remediation strategy on a portion of its infrastructure, to determine whether it resolves the problem before rolling out the fix more broadly. It also said the authentication component was impacting other services beyond Exchange.

User reports of the outage began streaming in around 11:30 a.m. ET on Monday, according to crowdsourced outage-detection site Downdetector, which was seeing north of 5,000 user reports by 2 p.m. ET; many other users complained directly on social media platforms like X. Those affected may see delays and failures sending or receiving messages, failures searching mailbox content, authentication errors, failures with mailbox operations, and other issues related to message delivery. As of 5 p.m. ET on Monday, Microsoft was still trying to resolve the problem.

Why it matters

The lengthy outage is a reminder of how much of the business world still runs on email, and specifically on Outlook and Exchange, making even a single authentication-component failure ripple across companies’ daily operations.