The ZEN Blocklist
The ZEN blacklist is Spamhaus’s combination zone. Over time, spamhaus has had several different methods for calling out multiple combinations of it’s zones. As it stands today, you can either chose to make DNS queries to individual zones as listed above, or combinations of them, or, use one zone, which includes them all. zen.spamhaus.org is the primary zone that contains all of Spamhaus’s data, and in turn, is the zone that most people use.
ZEN is the combination of all Spamhaus IP-based DNSBLs into one single powerful and comprehensive blocklist to make querying faster and simpler. It contains the SBL, SBLCSS, XBL and PBL blocklists.