Send Read Receipt - blind
Have the option for the email sender to see when the message is read, but do not give the recipient an option to not have the receipt sent.
Sandy Williamson commented
This would give the sender the impression tat the email had been read, when in fact it may have been accidentally clicked on by mistake, or by the feature that automatically amrks emails as read. A delivery receipt shold suffice to show the sender the mail has arrived.