Update the CSOM and REST APIs to allow email enabling of document libraries
With CSOM you can currently set the needed RootFolder properties:
rootFolder.Properties["vtiemailusesecurity"] = 1;
rootFolder.Properties["vtiemailsaveattachments"] = 1;
rootFolder.Properties["vtiemailattachmentfolders"] = "subject";
rootFolder.Properties["vtiemailoverwrite"] = 1;
but you can't update the EmailAlias of the parent List. The Rest API can't set the root folder properties or the EmailAlias.
We are moving to more towards the Groups inbox in the SharePoint Online to be the service for the emails. Storing emails in SharePoint libraries can cause certain challenges with the view limits etc. We are not looking to expose this capability using remote APIs. If you are using on-premises and would like to control these settings remotely, we would recommend to implement a custom web api for this specific usage.