As of my knowledge, once a sensitivity label is applied manually to an email, it should not change automatically unless there's a policy conflict or misconfiguration in your organization's sensitivity labels settings. Here are some steps that can help troubleshoot or resolve this issue: Check Label Policies: Verify whether there are any automatic labeling policies applied at the organization level that might be overriding your manual changes. An admin can check this under the 'Sensitivity labels' section of the Microsoft 365 compliance center. If such policies exist, discuss with your IT administrator about modifying them to avoid frequent overrides. Update Outlook: Ensure your Outlook client is up-to-date. Older versions of Outlook may have issues with sensitivity labels. Repair Office: Sometimes, repairing your Office installation can resolve unexpected behavior with Outlook and other Office apps. You can do this from the 'Apps & features' section of the Windows settings. Contact Support: If none of the above steps resolve the issue, contact Microsoft support for further assistance. They can help diagnose the problem more precisely using additional tools and access to logs.
Remember to always follow your organization's guidelines when dealing with sensitivity labels as they're critical for maintaining information security.