An email footer discouraging printing the email results in more pages printed and is counter productive from an environmental point of view
but
score: 3
we don't have any data showing how much of these warnings convincing people for not to print it. If they are protecting more papers then the extended ones it means that it's still working. Mail platforms should capture and hide them while printing.
Each email is one line longer, meaning that a whole extra pages is printed some times. Versus the change in peoples behaviour which there doesn't seem to be any evidence for.