Encrypted Email Not Viewable in Sent Items

Yes. The email is using Sensitivity Labels that were created in MS Purview and applied from Outlook. When the message is sent, it is then encrypted. What I discovered is that viewing the Sent Items in Web Outlook, the message was viewable. This only appears to be happening in the old Outlook Client. We enabled the new Outlook Client on the computer and obviously that resolved the issue. I would still like to understand if this is by design as Microsoft pushes everyone to use the new Outlook client or is there a configuration in the old Outlook client that can fix this.