In order to stop spam email and be effective a new standard will have to be implemented on how banning and related procedures are placed. All networks will have to start allowing MAC Addresses to be seen across networks and start banning by MAC Address.
If I wished to send out a million spam email messages I would first start by finding a server designation like mail.yourdomain.com then write a program to fake my email header to have ever one think I am from that server. I would then send to every known email address combination on every major email service I could think of.
If that email account don't exist that i was sending to I would not care as the bounced email is going to go to some dude's server and not me looking like they sent it to the internet as their email server header is the starting point. Now if the MAC address is readable through the entire process and also included in the networks ability to locate a particular mac address you will find where the spam is actually coming from and be able to block that MAC Address or even that networks IP Gateway.
If you really want to spam you can even hide your IP by using a proxy.
If you wanted a superior baning and filtering method you have to go by MAC Address as domain names and IP's can be spoofed to easily. To change a MAC address is not as easy as changing IP addresses. Every piece of network equipment in the world has a MAC Address and I have personally never seen two alike.
