Slicing Spam With Occam's Razor

To evade blacklisting, the vast majority of spam email is sent from exploited MTAs (i.e., Botnets) and with forged "From" addresses. In response, the anti-spam community has developed a number of domain-based authentication systems - such as SPF and DKIM - to validate the binding between individual domain names and legitimate mail sources for those domains. This paper explores an alternative solution in which the mail recipient requests a real-time affirmation for each e-mail from the declared sender's MX of record.