@Abhijith ClaySys - The above answer was correct till last week. But last week at Microsoft Build 2021 conference, we announced a new feature so that you can use Microsoft Graph with S/MIME, encryption etc. You may want to get it started from here.
secure (encrypted) mail API
Is it possible to send secured/encrypted emails programmatically using Microsoft Graph API? (Or any other APIs under the Microsoft product family). If yes, can you please share some documentation links for that?