outbound.appriver.com has no CNAME records.
Question and response
Question
dig outbound.appriver.com. NS
Answer
The response has no answer records.
Authority
appriver.com. 222 SOA hugh.ns.cloudflare.com. dns.cloudflare.com. 2397032929 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0