As an administrator of several forums I find this free service invaluable. Don't let the name fool you, this service offers much more than the other spammer blacklists. SFS often has extra context and evidence relating to banned users which other services do not have, this helps with spotting false positives. This blacklist uses a relational database system so is often able to match many seemingly random email addresses to the "real" email account. Fake domains and those only created for hosting a spam email server are marked as "Toxic", this is the same for any IP that is only used for spamming and botnets. The free API can be used with your own site or applications, and pre-made plugins are available for common site software. The well documented API is simple to use and can be accessed in a variety of ways to suit your needs. Worth noting: It is easy to have your self removed from the database if a **genuine **mistake has been made and you end up in it.