Technical listings occur mostly from mail-server configuration issues, such as missing or incorrect reverse DNS records, missing or incorrect banner greetings, and mail servers operating within a suspicious range of IP addresses.
Policy listings are based on an operator that does not wish to receive email from certain countries, or ISPs, that have a history of not honoring "unsubscribe" requests.
Evidence-based listings are those where the operator has received direct (or indirect) evidence that an IP address has been involved in sending unsolicited emails.