I am not a mail specialist, but would a simple solution not be to add an MD5 based checker in the mail ID. Before proceeding a mail the receiving party would call the "mailchecker" associated to the sending domain name to check the ID consistency (if there is a checker in the ID), what would also provide a real time receipt, ie a value added service pushing ISPs to implement the feature. I suppose it would also easily permit to determine if a quoted printed mail is a fake. This could be implemented transparently and progressively. This would add a relation but would decrease the processing and the storing of the spam: I suppose everyone would be winning. Servers without a "namechecker" update six months from now would be deemed suspicious. Sorry if this is a dumb proposition? jfc