server237.appriver.com has no CNAME records.
Question and response
Question
dig server237.appriver.com. NS
Answer
The response has no answer records.
Authority
appriver.com. 1592 SOA hugh.ns.cloudflare.com. dns.cloudflare.com. 2397032929 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0