Microsoft Investigates Outlook.com Sign-In Outage

Microsoft is investigating an ongoing Outlook.com outage that causes intermittent sign-in failures and prevents customers from accessing mailboxes.

Outage monitoring service Downdetector has received thousands of user reports since the incident began over three hours ago, with most citing login problems and connection issues.

In an update on its service health status page, Microsoft states that affected customers experience sign-outs and "too many requests" errors. "Some users may experience intermittent signin failures, including 'too many requests' errors or unexpected signouts," the company said.

Microsoft's investigation points to client sign-in scenarios as a possible contributor. The company is validating interactions across service components to identify next steps.

Microsoft has not disclosed the outage's root cause, affected user numbers, or regions. The incident is flagged as "service degradation," indicating noticeable user impact without full service downtime.

Last month, Microsoft mitigated an Exchange Online outage blocking mailbox and calendar access, and addressed separate Office.com and Microsoft 365 Copilot sign-in issues.