Rejecting during the SMTP session is a bad answer because IT ISN'T MADE TO BE USED AS A BLACKLIST. The whole purpose of the list is to gather statistics about how many domains have private whois info. Al Iverson is using it correctly to gather stats about domains. Also, don't trust SPF. Many legit sites don't use it or don't use it properly and spammers like to set "ip4:0.0.0.0/0" in their records.