smtp172prim.appshosting.com has no CNAME records.
Question and response
Question
dig smtp172prim.appshosting.com. NS
Answer
The response has no answer records.
Authority
appshosting.com. 600 SOA ns63.domaincontrol.com. dns.jomax.net. 2023092200 28800 7200 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0