Consider performing a
SpamAssassin Rule: URIBL_WS_SURBL
Standard description: Contains an URL listed in the WS SURBL blocklist
Explanation
The mail body contains a URI containing a domain that has matched an entry on the DNSBL Bill Stearns URI Blacklist (SURBL).
ws.surbl.org has records from Bill Stearns' former SpamAssassin ruleset sa-blacklist, plus some other manual lists.
Further Info
The default scores for this rule can be found in the online list of tests.
http://www.surbl.org http://www.sa-blacklist.stearns.org/sa-blacklist/