I created a draft EmailMessage (status = 5) and linked it to a case. After all approvals are done, the message should be sent. However, I cannot find a way to do this. The standard Messaging.sendEmail method can send instances of the SingleEmailMessage or MassEmailMessage classes, but not a record of the EmailMessage object.
How to send a prepared draft EmailMessage and make sure that is remains linked to the Case instance with the new status (sent = 3)?