Create a (non-draft) message via MIME content (like APPEND in IMAP)
We should be able to post MIME email content to create a new message (that isn’t a draft). Just to allow copying an email coming from another email account, which is a basic feature of any email client. In IMAP parlance, this is the APPEND command. It’s currently impossible to support this functionality when building an email client that uses the Microsoft Graph API.