SpamAssassin Rule: RCVD_IN_PSBL
Standard description: Received via a relay in PSBL
The last external relay in the Received chain was listed in the DNSBL The Passive Spam Blocklist (PSBL).
The Passive Spam Block List, or PSBL, uses the Spamikaze software, which works in a really simple way. If one of my spamtraps receives email from a certain IP address, then that IP address gets listed. After a certain time the IP address times out and is automatically dropped from the list.
The default scores for this rule can be found in the online list of tests.
See: https://psbl.org for details on removing addresses from this list.