E-mail spoofing based on the datalink layers and its application to e-mail aggregation systems: is it possible to make good use of e-mail spoofing?

It is well known that DHCP snooping is a famous countermeasure against DHCP spoofing. Actually, to what extent DHCP snooping can protect the DHCP clients from being injected malicious DHCP transactions running over the network segment? In this paper, we discuss the problem asking if there exists what is to SMTP spoofing as DHCP snooping is to DHCP spoofing, and the problem asking if it is possible for SMTP spoofing to be applied to a socially useful system..