Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may encounter Non-Delivery Report (NDR) failures when sending or receiving email messages – RESOLVED

Announcements Arpan Das

17/03/2025 08:37:00 AM

NHSmail Reference: INC46476230

Microsoft Reference: EX1030895

Issue Status: RESOLVED

Issue Description: Some users may encounter NDR failures when sending or receiving email messages in Exchange Online.

More info: Microsoft expect the impact to be mitigated for a majority of our users; however, they remain focused on ensuring this incident is fully resolved.
Users may receive a Non-Delivery Report (NDR) containing an error stating “554 5.6.0 Corrupt message content”.

Final Update: 25/03/2025 08:44:00 AM – Microsoft have completed their work to replay affected email messages and confirmed through service telemetry that NDR failure rates have returned to pre-incident thresholds; the service is maintaining a 99.99 percent success rate. If your organization continues to experience NDRs when sending email messages, we recommend contacting your support representative for further assistance.

Scope of impact: Some users serviced by the impacted portion of infrastructure sending or receiving email in Exchange Online may be affected, although impact is limited to a small subset of messages.

Next steps: Microsoft are examining the process by which they test and introduce changes to their caching logic to ensure caching issues aren’t introduced in future updates.