Servidores DNS Principal (mname) y Secundario (rname)
host: smtpworld.com
class: IN
ttl: 900
type: SOA
mname: ns-712.awsdns-25.net
rname: awsdns-hostmaster.amazon.com
serial: 1
refresh: 7200
retry: 900
expire: 1209600
minimum-ttl: 86400

Servidor de Correo
host: smtpworld.com
class: IN
ttl: 300
type: MX
pri: 5
target: mxbiz1.qq.com

Servidor de Correo
host: smtpworld.com
class: IN
ttl: 300
type: MX
pri: 10
target: mxbiz2.qq.com