SPAM bounce
What if the e-mail system had a SPAM bounce?
When I get mail ( POP3 ) I can get headers, download and delete. The sender can blindly send, request that it was received, get a notification that the e-mail is non existent.
I see the e-mail system modified as such:
If I mark a e-mail as SPAM the server should sent a rely to the sending server indication a SPAM rejection. If the sending server is the problem the receiving server bands the server. If the server isn't the problem it uses the SPAM rejection notice to deal with its clients, ( lock out, cleansing a compromised system, etc )