Microsoft Outlook.com Outage Causes Sign-In Issues for Users

Severity: Low (Score: 36.9)

Sources: support.microsoft.com, Bleepingcomputer

Summary

On April 27, 2026, Microsoft reported an ongoing outage affecting Outlook.com, leading to intermittent sign-in failures for users worldwide. The issues included unexpected sign-outs and 'too many requests' errors, impacting users' ability to access their mailboxes. Microsoft indicated that client sign-in scenarios may be contributing to the problems but has not disclosed the root cause or the number of affected users. The company flagged the incident as causing 'service degradation,' a term used for issues with noticeable user impact that do not take the service offline entirely. By April 28, Microsoft confirmed that service health had returned to normal but required iPhone users to manually re-enter their credentials to regain access. The incident follows a series of previous outages affecting Microsoft services, including Exchange Online and Microsoft 365 Copilot. No specific attack vector or exploitation method was identified in the reports. Key Points: • Microsoft's Outlook.com outage began on April 27, causing widespread sign-in issues. • Affected users experienced unexpected sign-outs and 'too many requests' errors. • Microsoft required iPhone users to re-enter credentials to regain access as of April 28.

Key Entities

• Zero-day Exploit (attack_type)
• Office.com (platform)
• outlook.com (domain)