It is new. It's not just convenience. It's the aspect of control - think about it: you can control who is looking at the contents of an email even if they have forwarded it on to 1, 2, 3 or more people. You see who is looking at it and if you don't like that, you can vaporize it with the touch of a button. That's of great value for a lot of industries.

I saw this article on the Envilope website and it made me think of how many times in business people send emails to the wrong people...their features could saw a lot of headaches.

Wrong Turn In Brazil - https://blog.envilope.com/wrong-turn-in-brazil-the-envilope-solution/