Servidores DNS Principal (mname) y Secundario (rname)
host: dishnetworkmail.mobi
class: IN
ttl: 900
type: SOA
mname: ns-1896.awsdns-45.co.uk
rname: awsdns-hostmaster.amazon.com
serial: 1
refresh: 7200
retry: 900
expire: 1209600
minimum-ttl: 86400