Save email from Outlook Online to SharePoint library through an AddIn

I have a requirement to a selected email(s) to Outlook through an Add-In. I need it to work with the Outlook client app as well as Outlook Online. I put together a simple VSTO plugin in the Outlook client app which works but I want to do this through an Add-In now.

I have been through this tutorial to save email attachments to OneDrive which has similar functionality. Attachments to OneDrive Git

I like the functionality of this and would like to save emails to SharePoint the same way.

Does anyone have a good tutorial for doing this? Or a reference for the libraries? I’ll post my progress for others as I get through it. I just haven’t been able to find exactly what I’m looking for with this.