Some users’ incoming email messages are being quarantined unexpectedly in Exchange Online

Title: Some users’ incoming email messages may be quarantined unexpectedly in Exchange Online

User impact: Users’ incoming email messages may have been quarantined unexpectedly in Exchange Online.

Final status: Following our review of system telemetry, as well as header logs of sample messages, we’ve assessed that a Domain Name System (DNS) configuration issue resulted in impact. We’ve corrected the DNS configuration and confirmed through telemetry that impact has been remediated.

Scope of impact: Some users’ incoming email messages may have been quarantined unexpectedly in Exchange Online.

Start time: Tuesday, September 26, 2023, at 5:16 PM UTC

End time: Tuesday, September 26, 2023, at 11:30 PM UTC

Root cause: A DNS configuration issue resulted in impact.

Next steps:
– We’ll continue to review the context surrounding the offending DNS configuration change to help us better understand the source of the problem and prevent similar impact in the future.

This is the final update for the event.