Bwa ha ha ha ha. I guess the perception is different depending on where you're from. I immediately thought of the swipe left/right aspect - though I'm in a community that is more chaste than most though. For example, I know a couple who met through tinder without any sex before marriage. That's probably why I thought different - I just really haven't known enough people who use tinder like you described. Or used tinder at for that matter.
My confused impression when I read the title was "A sex hook-up app that uses e-mail?"