mx1.666.net has one IP number. mx1.69.net, mx1.um.net, mx1.ab.net, mx1.yl.com, mx1.a1.com and at least 100 other hosts point to the same IP. 666.net use this as a mailserver. 666.net is delegated to two nameservers, however both delegated nameservers are missing in the zone and two other nameservers are listed instead. Some of them are on the same IP network. Incoming mail for 666.net is handled by one mailserver at 666.net themselves. 666.net has one IP number.