mail.sevstar.net has no CNAME records.
Question and response
Question
dig mail.sevstar.net. NS
Answer
The response has no answer records.
Authority
sevstar.net. 4978 SOA ns.sevstar.net. admin.sevstar.net. 1772698800 3600 7200 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0