The "Truncate" DNSBL (zone truncate.gbudb.net) lists IPv4 addresses that have been observed transmitting "email containing spam, scams, viruses, or other malware based on statistics in the global GBUdb network." This "Good, Bad, Ugly database (GBUdb)" is a "real-time collaborative IP reputation system," based on statistics collected by email threat protection software Message Sniffer.
If you're listed on the Truncate DNSBL, can you request removal? No, explains the website. IP addresses are removed automatically, usually within a couple of days of the bad activity having ceased. They warn, however, that in some instances, if enough bad activity was denoted, it may take longer for an IP address to automatically disappear from their list.
Have any more information you'd like to share about this blocking list? Please feel free to contact me and I'll be happy to update this page with your additional information.