I wouldn’t use valid to describe an MX that starts with:
That is a telltale sign of an MX that is pointed at a proxied hostname. RFC 5321 4.1.2 prohibits use of the underscore character in MX hostnames. It is preferable to use a dedicated hostname such as mail.example.com and set it to DNS Only.
Ah interesting, my bad, I hadn’t ran into that before.
I’m guessing that RFC is another one that is ignored, just for fun I tested sending to a proxied address like that from gmail and it still worked.
I would for sure clean that up/make an unproxied hostname like he’s suggesting. It does look like 126.96.36.199 is the right IP though, matches the one you shared & has smtp open. Any other info would be helpful.