Overview

• Microsoft confirmed full Outlook service restoration by 17:25 UTC on July 10 after configuration changes fully saturated all affected infrastructure.
• Preliminary diagnostics identified an underperforming mailbox infrastructure and a failing authentication component as the outage’s root causes.
• The outage disrupted email, calendar and contacts access for millions of users worldwide across web, desktop and mobile platforms.
• Users encountered various errors including invalid licenses, 500 internal server failures and 401 unauthorized messages during the disruption.
• The episode highlights growing dependence on cloud-based communication tools and follows multiple Microsoft 365 outages earlier in 2025.