MX

MX adds an MX record to the domain.
Priority should be a number.
Target should be a string representing the MX target. If it is a single label we will assume it is a relative name on the current domain. If it contains any dots, it should be a fully qualified domain name, ending with a ..
dnsconfig.js
D("example.com", REG_MY_PROVIDER, DnsProvider(DSP_MY_PROVIDER),
MX("@", 5, "mail"), // mx example.com -> mail.example.com
MX("sub", 10, "mail.foo.com.")
);