|There may be a setting you could put in sent mail requesting a response when opened but it is always at the option of the recipient.|
Email privacy should be no different that snail mail. You can send a letter but there is no way you can verify the addressee opens the envelope or just confines the message to the trash. I use Mailwasher for just that purpose. It retrieves only the header of incoming mail and if I am not interested in the content I just blow it away without opening the complete message.
Goin' Fishin' (Some day)