mx.postmail.globalhost1.com has no CNAME records.
Question and response
Question
dig mx.postmail.globalhost1.com. NS
Answer
The response has no answer records.
Authority
globalhost1.com. 1611 SOA aarav.ns.cloudflare.com. dns.cloudflare.com. 2397344346 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0