It appears to be "Yes."  The receiver either never receives the mail, just a link to the mail on the Dmail server that the SENDER can delete OR the receiver reads the mail locally using the Dmail extension in their browser.  The Dmail extension lets the sender decide if they want to delete the sent mail, even if it's already been read by the recipient.  I guess the recipient can copy/paste/download the mail but maybe the electronic signature is deleted so there is no longer proof of who sent what when