As Monique said, this is the native behavior of proof, in that the email
is generated to a specific user, and that specific link is to that
user's log in. We have had to train our users NOT to forward the email
proof. You will also find that if the "forwarded user" makes comments or
decisions on the Proof, the display will indicate that those changes and
approvals were made by the original email recipient. I had to track this
issue down, as we had this happen in our environment. I'm not sure if
...