mx.nixihost.com has no CNAME records.
Question and response
Question
dig mx.nixihost.com. NS
Answer
The response has no answer records.
Authority
nixihost.com. 1306 SOA elmo.ns.cloudflare.com. dns.cloudflare.com. 2396760976 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0