There is a solution which I havent applied yet because it seemed for a single account. Is it possible to go for these steps twice to get read receipt for two accounts, depending on which has sent the email?
I think which the solution is emulate to MailTrack.io
i.e. add a invisible image hosted in cloud and to be verify if it was requested. But I don't know if it is posible in Outlook for Mac 2011.