Microsoft Exchange Online outage blocks access to mailboxes

Microsoft reported and investigated an Exchange Online outage impacting Outlook on the web, Outlook desktop, Exchange ActiveSync and other connection methods that prevented some users accessing mailboxes and calendars; the company mitigated the Exchange Online disruption but continues to investigate a related Office.com / Copilot web sign‑in issue. Microsoft’s status updates note networking infrastructure inefficiencies as the root cause under investigation and recommend using app-based Copilot services while web sign‑in is affected.