So why not just group people by email address? The public email providers can just have their own group as do the private ones, and if people wanna join the gma

So why not just group people by email address? The public email providers can just have their own group as do the private ones, and if people wanna join the gmail group for some reason... who cares? Or just block the big ones (gmail, yahoo, outlook) and call it a day. I don't think this is a problem you're going to solve the way you want to.