Overview
- The incident was logged in the Microsoft 365 Admin Center as EX1464935 and began at 17:53 MESZ on Monday, when users worldwide started reporting login failures and mail send/receive errors.
- Microsoft traced the disruption to a central authentication and connection component inside Exchange Online and developed a mitigation that technicians are testing on a subset of servers.
- Engineers have begun a gradual rollout of the update to affected servers while continuing diagnostics, so service restoration will proceed in phases rather than all at once.
- Users reported tens of thousands of outage complaints on monitoring sites and experienced mailbox sync failures, frozen clients, and problems in admin consoles; experts advise not to change local settings or repeatedly resend messages to avoid duplicates.
- Exchange Online is a core email service for businesses and consumers, so continued disruption could delay business workflows and administrative tasks until the phased fix completes and is verified.