If I understand that thread correctly, that is for e-mail addresses in body text?
I'm suggesting looking only at authenticated UID's in headers from specific providers like Yahoo who are notorious for spam, but their MTA's also send a significant amount of ham so we cannot DNSBL block them. Given that we know the UID's cannot be spoofed (if we verify the delivery with DKIM), such a BL can be safely populated in an automated fashion using spam traps. So this might be more of a "Authenticated User RBL". Warren