Some users’ email messages may not be quarantined and fail to be stored in the quarantine folder

Timeline

Every update Microsoft posted for this issue, newest first.

1. Nov 5, 2026, 23:23 CET

   A post-incident report has been published.

2. Nov 5, 2026, 23:23 CET

   A post-incident report has been published.

3. Oct 2, 2026, 19:46 CEST

   We completed deployment of our fix to the affected environments and confirmed with affected users that this action successfully resolved the problem.

4. Oct 2, 2026, 00:01 CEST

   We're continuing to monitor the deployment of our fix, which has reached 88 percent saturation to the affected environment. We anticipate the deployment will complete by our next scheduled communications update.

5. Oct 1, 2026, 19:35 CEST

   We've initiated the fix release and are monitoring as it progresses. We expect to have a completion timeline by the next scheduled update.

6. Oct 1, 2026, 03:02 CEST

   Validation of our fix is in its final stages, and we expect to begin deploying it to the affected environment by our next scheduled update. We’ll provide an estimated completion timeline once available.

7. Oct 1, 2026, 03:02 CEST

   Validation of our fix is in its final stages, and we expect to begin deploying it to the affected environment by our next scheduled update. We’ll provide an estimated completion timeline once available.

8. Sep 30, 2026, 20:20 CEST

   We've identified a recent service-side update that introduced an impacting code error that's causing some email messages to not be quarantined and fail to be stored in the quarantine folder. As we develop a code fix to remediate the impact, we're exploring a secondary potential mitigation option involving moving affected service traffic. We're expecting more clarity into our mitigation action plan by our next scheduled communication update.

9. Sep 24, 2026, 23:49 CEST

   A recent service-side update unintentionally introduced a code error that is causing legitimate email messages to be incorrectly quarantined and not delivered to recipients. We're developing a code fix and actively validating and testing the remediation in our test environment before broader deployment. We expect this validation work to be completed before our next scheduled communication update.

10. Sep 24, 2026, 20:40 CEST

    We've received the requested network message IDs (NMIDs) for failing email deliveries and are analyzing them in order to assist with our ongoing root cause investigation.

11. Sep 24, 2026, 16:58 CEST

    We're analyzing potential email processing failures from the provided message IDs. We're working with some reporting users to collect and provide network message IDs (NMIDs) from failing email deliveries to assist with our troubleshooting analysis.

12. Sep 24, 2026, 15:17 CEST

    We're reviewing message IDs to help determine the next steps to reach a mitigation plan and root cause analysis.

13. Sep 24, 2026, 13:41 CEST

    We're reviewing support case details to determine our next troubleshooting steps.