[boplicity]

> forcing a financial cost to sending mail

By doing this, you'll encourage the commercialization of email. The people who can fund sending email will be the ones who send email.

Frankly, I don't think email is broken, as is. It is very easy to subscribe and unsubscribe to email lists, and spam filtering generally works. It is relatively easy to control one's inbox, and it is completely under your control, as opposed to the many other services that have tried to replace it.