mail.ar66.xvserver.com has no CNAME records.
Question and response
Question
dig mail.ar66.xvserver.com. NS
Answer
The response has no answer records.
Authority
ar66.xvserver.com. 281 SOA ns1.xvserver.com. hostmaster.ar66.xvserver.com. 2019020102 14400 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0