Outlook 365 client vs Microsoft Graph API

[MustangProgrammer]

Does anyone know if the Outlook 365 Client is communicating with the cloud using some sort of MAPI or is it using HTTP like Microsoft Graph?  Trying to determine why the Microsoft graph portion of my application is failing.  I am not getting sender or from fields on my queries.  Is there something I'm missing?  Is there a way for me to compare the email that is failing in my app to the outlook client on a lower level?

[#2]

You'd better debug your app using the GRAPH explorer. Forget about Outlook.

[#3]

It depends on which client, but let’s assume we’re talking Outlook on Windows then yes, it will likely use MAPI over HTTP.

Which Graph API resource are you using? If specific attributes are not returned, did you try to force them to be returned using the $select operator?