Spamhaus has combined the SBL, XBL and the PBL blocklist into one single powerful and comprehensive DNSBL called zen blocklist to make querying faster and simpler. As advised by Spamhaus, I have changing the settings in my server to query zen instead of SBL and XBL.
There is an interesting story on the name "Zen". Zen was guard dog and for many years it guarded Spamhaus's base in England. After giving the name to the most powerful DNSBL, Zen now guards our networks and customers.
