The only way I can see this kinda working at all would be for certain servers.

Like if you had a very important email you wanted to send to someone and it needed to stay secure and stuff, I can see paying that just to make sure it doesn't get lost or misdirected.

But there isn't any way to charge people for email unless it is just off certain servers. How are they going to be able to know how many emails are getting sent off of my email server from home? Now that would be invasion of privacy....