As it was explained to me, the worry was less about actual exploits and more to do with supporting various HTML features in the respective clients (Think Canius

As it was explained to me, the worry was less about actual exploits and more to do with supporting various HTML features in the respective clients (Think Caniuse, but specifically for email). Back when I was doing some work in this area, the Email Standards Project was trying to get most of the popular clients to update their rendering engines with this goal in mind. So far as I can tell, this work seems to have been inherited by the people behind the Email Markup Consortium.[1] [1]: https://emailmarkup.org https://emailmarkup.org