What if sending an email cost a penny?
Not a lot. Just enough that you’d think twice before hitting reply all.
Spam would vanish overnight, since it only works because sending a million messages is free. Newsletters would get shorter and better. And the inbox might go back to being a place where people write to each other.
The obvious problem is who gets the penny. The fun version: the recipient does. Then a busy inbox is a small income, and every message you send is a tiny gift.