and this, http://www.spamhaus.org/zen
"Caution: zen.spamhaus.org replaces sbl-xbl.spamhaus.org. If you are currently using sbl-xbl.spamhaus.org you can now replace 'sbl-xbl' with 'zen' (sbl-xbl.spamhaus.org will eventually become obsolete and may in the future be withdrawn from service). zen.spamhaus.org should now be the only spamhaus.org DNSBL in your configuration. You should not use ZEN together with other Spamhaus blocklists or you will simply be wasting DNS queries and slowing your mail queue."
