Have an image stored on a server... Monitor the number of hits on that image, gives you a good approx. of the amount of times the email was viewed.
Preferably ,send your email text as an image, so they don't have the choice to load it to view the email.
I've been using this tactic, mixed with a script that kills the image after 1 view, which pretty much prevent anyone from reviewing nor forwarding that email.
Yeah.... What are you sending in your emails? If you have something that needs to remain private, then send it to only people you trust. If its busniess related. All business that are worth anything have privacy laws, that if you forward it to a person " not " supposed to see it you can get sued. Among other things. I know my work has it.
