Microsoft has confirmed that a major Exchange Online outage has been mitigated, restoring access for users across the globe who were unable to reach their emails and calendars.
🔍 Timeline of the incident:
- Sept 11 (Morning, EDT): Users began reporting issues via DownDetector, unable to connect to Outlook, Teams, and Hotmail.
- Microsoft identified high CPU utilization on the affected infrastructure, likely tied to a specific software build causing repeated database failovers.
- Sept 11 (Evening): Engineers applied configuration changes, leading to signs of recovery.
- Sept 12 (Early AM): Microsoft announced that services were back to optimal levels, with continued monitoring.
📌 User Impact:
- Failed mailbox logins
- Delays in email delivery
- Calendar & Outlook mobile crashes (esp. Hybrid Modern Authentication users on Android/iOS since Aug 17)
✅ Resolution:
After restoring degraded infrastructure, Microsoft confirmed the root cause as a recurring issue with a faulty software build, which triggered repeated dismounts and message queue buildups. The problem has now been mitigated.
📢 Microsoft continues to monitor the environment and is rolling out additional fixes to prevent future recurrence.
At Alcaeus Services, we help organizations navigate outages, strengthen continuity planning, and ensure resilient access to business-critical cloud services.
