Registro DMARC
v=spf1 mx a ptr include:mailgun.org -all

Servidores DNS Principal (mname) y Secundario (rname)
host: mtoverland.com
class: IN
ttl: 21600
type: SOA
mname: ns-cloud-d1.googledomains.com
rname: cloud-dns-hostmaster.google.com
serial: 6
refresh: 21600
retry: 3600
expire: 259200
minimum-ttl: 300

Servidor de Correo
host: mtoverland.com
class: IN
ttl: 3600
type: MX
pri: 10
target: mail.widesol.com