I have a client whose existing setup allows them to upload emails directly from Outlook to their own DMS using an Office addin (2010). They want to migrate the DMS to SharePoint Online and part of that move will possibly be to preserve this functionality; that is, the ability to upload the actual .eml/.msg files directly, not just the attachments.
Obviously Incoming Email is gone in SPO so that isn't an option, and using 'Open with Explorer' to drag and drop the files, while technically suitable, is a bit clunky. 365 Groups is fine for email attachments, but not for the actual emails.
I'm guessing some sort of Outlook addin is what would be required (ideally one that can be used with Outlook Online as well as the Office 2016 desktop app) but not sure where to start with this. Can anyone provide some guidance on how to go about this, or even some examples of existing code that could do the job?