MX is a numeric IP

[Kevin Darcy]

Tech W. wrote:
> What will be happened if a MX is an numeric IP?
> for example,
>
> # dig vip.online2.sh.cn mx +short
> 10 218.1.71.125.
>
>   
It's syntactically valid.

But, since there is no "125" top-level domain, or, obviously, any 
subdomains of of that domain, semantically it's incorrect.

To put it another way, it's a correctly-formed record, pointing at 
something that doesn't exist.

It's also a flag that expresses "hey everybody, I don't know how to edit 
zone files properly!".

- Kevin