The LashBack DNSBL
The Unsubscribe Blacklist (UBL) is a real-time blacklist of IP addresses which are sending email to names harvested from suppression files. LashBack has been in operation since 2003. Spammers deploy what are known as suppression lists, also known as unsubscribe forms. When a spam is sent with a link to unsubscribe you address from the mailing, your address should in theory be removed. Often times, the opposite happens, and your address is then considered more valuable, and resold to other spammers as a known deliverable address.
ubl.unsubscore.com has systems in place that will use trackable email addresses to unsubscribe from the suppression lists. Over time, they can track which suppression lists are good, and which are actually sharing their suppression lists with other spammers. When this type of activity is apparent, the IP address of the sender is added to the DNS blacklist.
LashBack’s UBL only lists the IP addresses of senders who are using email addresses harvested from suppression lists.