Another cure that is worse than the disease
Ha! I've used that to describe spamhaus and their minions... Years ago I had a client who ended up getting blocked randomly because (drumroll please) spamhaus added an entire /22 to their IP blocklist! The client's /29 was inside that block, so naturally they got blocked by anybody honoring spamhaus' block list... (And to the legion of assholes that troll anybody criticizing spamhaus' slipshod work and labels them a "spammer," Fuck you! They didn't send any spam, EVER. And blocking an entire /22 (covering some of a datacenter's customers, but not others) is arbitrary to the point of negligence.
When it had all played out the /22 block was a result of (wait for it!) a disgruntled employee at the datacenter exploiting Spamhaus' notoriously weak quality-control to screw-over his former employer with an annoying, somewhat hard to identify problem... Annoying because spamhaus will keep blocking it in perpetuity until somebody figures out how to make them stop. Somewhat hard to identify because it wasn't every client having problems, and the ones having problems weren't having it with all recipients. Now, of course, we know that description of symptoms can easily be an RBL run amok... Of course then the question becomes "which one?"
I don't like spam any more than the next guy, but dealing with the shrill assholes who have made it their life's work to fight spam (hint: When somebody tells this to you, FFS, don't laugh!) is just one step less-unpleasant than repeated, unneeded root canal... The high and mighty, pompous, and arrogant attitudes (anybody who disagrees with us is stupid or a spammer!) make the low-quality of the work produced that much more glaring. Honestly, haven't you people ever heard of IronPort, Barracuda, or MXLogic? Seriously: Get a life. Reporting each spam individually is the least efficient way to fight the problem. What makes it worse is when you tell these Don Quixote types that they're wasting their lives they accuse YOU of being a spammer!