SpamhausEdit

Spamhaus is one of the most reputable and accurate DNS-based blacklists used to combat spam.

Their SBL Advisory is "free for individuals operating small mail servers as long as your email traffic is low". Their XBL advisory is also free for users with "normal mail servers". Paid yearly subscriptions are available for other users not falling into these categories.

See also

• Official website: http://www.spamhaus.org/
• "Guide to Effective Spam Filtering for Networks": http://www.spamhaus.org/effective_filtering.html