Spamhaus Block List (SBL)
The Spamhaus Block List Advisory is a database of IP addresses from which Spamhaus does not recommend the acceptance of electronic mail.
The SBL is queriable in realtime by mail systems thoughout the Internet, allowing mail server administrators to identify, tag or block incoming connections from IP addresses which Spamhaus deems to be involved in the sending, hosting or origination of Unsolicited Bulk Email (aka "Spam"). The SBL database is maintained by a dedicated team of investigators and forensics specialists located in 10 countries, working 24 hours a day to list new confirmed spam issues and - just as importantly - to delist resolved issues.
We monitor this blacklist since 2015-01-01. More information: http://www.spamhaus.org/sbl/