International registry of sold computer hardware and MAC addresses? Ouch. That's a little on the Orwellian side for me. A slightly less intrusive option might be an optional cryptographic signature in a central repository somewhere. The keyword there being optional. Server software could be configured to handle signed/valid mail differently from unsigned mail. M$ has enough marketing leverage to initiate an anti-spam campaign along the lines of "end spam! add your (or your mail-server's) signature to the ...." The hard-part for m$ would be implementing in a way that competitive MTAs (GNU implementations etc...) could utilize a system like that.

<snip>
> information regarding the physical MAC addresses of spammers
> (which could be compared to an international registry of sold
> computer hardware) or other "absolute" information could be
> included. I don't really know too much about where email
<snip>

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