His mate is a wise man. RBLs are a really terrible idea, and
they've caused a lot of valid mail to be rejected. There's really
no way to reliably determine that a message is spam based on the IP
address or sender's domain name. The most you should do with RBLs
is delay or rate-limit mail from the blacklisted sites, you should
never reject such mail.
It's never clear to me what Keith Moore means by "RBL" when he repeats
that claim. Those three letters are a registered service mark for a
product that historically has been run so conservatively that claims
that should not be used to reject mail sound silly.
Yes, "RBL" did indeed reject valid mail, because it misled site
administrators into thinking that mailers that failed its test were
inherently able to be exploited into relaying significant amounts of
spam. So sites that trusted RBL's misrepresentation blocked valid mail
from sites that rate-limited relayed mail (including the site I ran at
one time) even when that rate-limiting was an effective spam block.
I really have no sympathy for net vigilanties who insist on trying to
enforce their own narrow-minded definitions for how the net should work,
and who disrupt others' service in the process.