Extract the plaintext bytes from message attachments (.rpmsg) using InspectAsync()

Question

I'm using MSGraph to pull in message data from our mail server and save to our internal db for later use. The issue we are running into is when trying to extract attachment bytes from .rpmsg files using the InspectAsync() call from the Microsoft Information Protection library.
The InspectAsync() call throws an exception: 'File type cannot be inspected'

                    string email = "Tst@test.com";  
                    var engineSettings = new FileEngineSettings(email, authDelegate, "", "en-US");  
                    engineSettings.Identity = new Microsoft.InformationProtection.Identity(email);  
                    var customSettings = new List