dfw-s04.nixihost.com has no MX records.
Question and response
Question
dig dfw-s04.nixihost.com. MX
Answer
The response has no answer records.
Authority
nixihost.com. 1800 SOA elmo.ns.cloudflare.com. dns.cloudflare.com. 2396760976 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0