mail.advancedserverdns.com has no CNAME records.
Question and response
Question
dig mail.advancedserverdns.com. NS
Answer
The response has no answer records.
Authority
advancedserverdns.com. 1752 SOA gabe.ns.cloudflare.com. dns.cloudflare.com. 2398144655 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0