As a receiver of email why would I want to receive a responsive email? What does it mean for me? And how will it look in Thunderbird, etc., when received from someone not on my trusted list?
It means it will look good in Thunderbird and Gmail for Android. Thunderbird will render custom CSS it won't load any external resources though (e.g. images). Maybe it's a nice idea to add preview to this tool how would it look like on Thunderbird and mobile.
