The url for the website is: <http://www.mxtoolbox.com/blacklists.aspx>
ABOUT BLACKLIST CHECK
This test will check a mail server IP address against 147 DNS based
blacklists. (Commonly called Realtime blacklists, DNSBLs or RBLs).
If your mail server has been blacklisted, some email you send may not
be delivered. Blacklisting is a common (although largely
ineffective) way of reducing spam. If you don't know your mail
server's address, start with a MX Lookup.
http://www.mxtoolbox.com/index.aspx