ns72.worldnic.com has no MX records.
Question and response
Question
dig ns72.worldnic.com. MX
Answer
The response has no answer records.
Authority
worldnic.com. 1800 SOA heidi.ns.cloudflare.com. dns.cloudflare.com. 2396669004 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0