I agree with the article, but I would go even further. This whole thing is stupid. You physically
can’t put an IP address into an MX DNS record. What the syntax (perhaps misleadingly) allows is to put a domain name there with labels consisting of only digits. That is, the “IP adress” 1.2.3.4 you wrote in your MX record is actually the domain name "1.2.3.4.yourdomain.com" with “1”, “2”, “3”, “4”, “yourdomain”, and “com” as the individual domain labels. There is no way to actually store an IP address in an MX DNS record. It just so happens that the usual syntax for IPv4 addresses turns out to be valid syntax for an (unrelated) domain name as well.
And, of course, if you try to write an IPv6 address, it will naturally fail, since IPv6 addresses uses colon “:” characters, which are not allowed in domain names.
Therefore, it would be beyond silly for programs to actually use these invalid domain names in MX records. MX records which point to domain names which cannot be resolved are simply broken.
And, of course, if you try to write an IPv6 address, it will naturally fail, since IPv6 addresses uses colon “:” characters, which are not allowed in domain names.
Therefore, it would be beyond silly for programs to actually use these invalid domain names in MX records. MX records which point to domain names which cannot be resolved are simply broken.