At this point he can then run the mail through a series of weighted RBLs.
Fuck you and your RBLs. RBLs are a draconian solution that do immeasurable damage to those of us who (1) aren't spammers, and (2) choose to run our own mailservers on business-class IPs. I can't tell you how many times various IPs I use for outbound mail (I run several mailing lists) end up on an RBL for absolutely no fucking reason.
Oh, because someone in the same /24 block sent spam? Really? That's a good reason to block an entire /24 subnet?
RBLs are a solution in search of a problem. Some of them are nothing more than moneymakers for the people that run them: In order to get off their list, they blackmail you into paying money.
Want to do the world a favor? Don't use RBLs. You'll just end up finding yourself blacklisted at some point anyway.