Definitely a problem that should be fixed. We have seen cases (plural) where 3rd party black lists used by some of the big players have decided to ban large chunks of the IPv4 address space.

But at least these black lists are visible. The worst ones, as the author alludes to, are the non-public black lists that quite often are within the large email providers themselves. It takes a while to figure out you are on one of these and then good luck getting off it.