PSBL is an easy-on, easy-off blacklist that does not rely on testing and should reduce false positives because any user can remove their ISP's mail server from the list.
The idea is that 99% of the hosts that send me spam never send me legitimate email, but that people whose mail server was used by spammers should still be able to send me email.
This results in a simple listing policy: an IP address gets added to the PSBL when it sends email to a spamtrap, that email is not identified as non-spam and the IP address is not a known mail server.
Removal of IP addresses from the list can be done by anyone. Remember, PSBL lists IP addresses, not email addresses, so please put an IP address into the box. A legitimate user unlucky enough to share a server with spammers can easily remove their own mail server from one or two lists. Spammers, on the other hand, would have to remove the email servers they use from thousands of lists, which is far too much work.