If you are on the Truncate Blacklist, there could be any number of issues that need to be addressed in your network: virus-generated spam, dynamic IP addresses previously used by spammers, or bulk mail sending that does not comply with the CAN-SPAM Act.
Truncate Reports Sources Of Spam
Spam-based Blacklists are those that will list either single IP Addresses or entire ranges that have actually received Spam, i.e. Unsolicited Bulk Email (UBE) in their Spamtraps from an IP-Address. This could be a result of a compromised email account, an Open Relay, or simply sending mass emails / marketing and not following best practices according to the "CAN-SPAM Act of 2003" (ref: https://en.wikipedia.org/wiki/CAN-SPAM_Act_of_2003)
Truncate Reports Virus Infected Sources
Virus-based Blacklists are those that will list single IP Addresses (or hostnames) of email servers that have sent Spam traffic that is generated by some form of a Virus, Malware, Trojan, or "botnet" infection in a network. This is often a result of a user visiting a webpage that houses an infection and downloads malware on a PC which then creates a "mini SMTP" server used to hijack account information, and send bulk email to recipients in the Users' email address book. It can affect the actual machine housing the "Email server platform" or on a local PC which is allowed to connect to the Email Server IP Address on SMTP port 25.
Truncate Automatically Delists Entries
This blacklist does not offer any form of manual request to delist. Your IP Address will either automatically expire from listing after a given timeframe, or after time expires from the last receipt of spam into their spamtraps from your IP Address.