Since Ethernet strings die, I give you my opinion of how to stop SPAM. We shall let Ethernet defend for itself for now. It is doing fine w/o my help.
Mail Adminstrators need to have peering policies. Traffic Adminstrators need to have traffic policies. Processes beget policies. These policies need to be enforced by protocols. If two peers are authenticated as valid communications agents by the mail transfer protocol, they should be given a higher thread of priority than random email by someone telneting to the server (ex.). As with PIM Snooping, Ethernet based networks can easily snoop this activity (authenticated traffic) and deny it at wirespeed as close the source as you dare go (domain). These service could easily be positioned in the core if you are already pumping the packets to an FPGA. Going to an ASIC may be a bit more difficult. 10G is an FPGA.