Spam and Open relay systems - Spam (SORBS-SPAM)
The SORBS (Spam and Open Relay Blocking System) provides free access to its DNS-based Block List (DNSBL) to effectively block email from more than 12 million host servers known to disseminate spam, phishing attacks and other forms of malicious email. The list typically includes email servers suspected of sending or relaying spam, servers that have been hacked and hijacked, and those with Trojan infestations. In an attempt to provide preemptive protection, SORBS also lists servers with dynamically allocated IP addresses.
Listing is manual and is performed when any spam is received at a SORBS spamtrap. SORBS spamtraps include, but are not limited to, the private email addresses of the SORBS administrators. On occasion, when a particular network is seen to be spamming and the listing of a single IP address seems to have no effect, increasingly larger sections of the Netblock will be listed. If spamming continues, the size of the listing will be slowly expanded (depending on the number of spams received) until something is done about the spammer.
We monitor this blacklist since 2015-01-01. More information: http://www.sorbs.net/