Check IP on RBLs
This service checks if an IP address is listed in the Relay Black Lists (RBLs) used to fight spam by antispam software. RBLs are a distributed system to track spammers and to fight actively spam. Actually many softwares use them to know if a particular mail message has been sent from an ip address known to send spam. This tool currently supports the best Relay Black Lists around there and you can find checks for all the RBLs used by Spamassassin on his spam fight activity. Clicking on the removal link you will be taken directly to the Black List's removal tool.