> Why didn’t the DMARC spec say that a domain is “not present” if it lacks MX records?
That doesn't match the SMTP spec, RFC 5321 says
> If an empty list of MXs is returned, the address is treated as if it was associated with an implicit MX RR, with a preference of 0, pointing to that host.
That doesn't match the SMTP spec, RFC 5321 says
> If an empty list of MXs is returned, the address is treated as if it was associated with an implicit MX RR, with a preference of 0, pointing to that host.
https://www.rfc-editor.org/rfc/rfc5321.html#section-5