Some users may encounter Non-Delivery Report (NDR) failures

Update timeline

1. identified Mar 18, 2025, 10:44 AM UTC

   We have been advised of potential service disruption to Microsoft 365 services. Some users may encounter Non-Delivery Report (NDR) failures when sending or receiving email messages. Microsoft engineers have confirmed that deployment of a fix is progressing as expected, with the majority of impact already mitigated. However, the remaining affected infrastructure may take additional time to update completely. If you are experiencing email delivery issues, please reach out to us. Further updates will be posted as soon as they become available.

2. identified Mar 19, 2025, 11:55 AM UTC

   Microsoft are reporting that the additional mitigations have reduced the volume of intermittent failing messages. They will continue to monitor to ensure service returns to normal.

3. identified Mar 20, 2025, 02:18 PM UTC

   Microsoft have reported that they have made steady progress with the new fix, which has been developed and is being tested internally before release. The new fix will be deployed once internal testing is complete.

4. monitoring Mar 24, 2025, 10:52 AM UTC

   Microsoft have advised that a rollout of an updated fix has been applied to all tenants and has saturated. For emails remaining that have not been sent, these will be resent. Microsoft are continue to monitor to confirm the fix has resolved the issue completely.

5. resolved Mar 25, 2025, 04:21 PM UTC

   Microsoft have confirmed that the fix has saturated all environments and all unsent email has now been processed. Systems have returned to normal operation.