Apex domains cannot have CNAME records.
Question and response
Question
dig csmaildealer.com. NS
Answer
csmaildealer.com. 5 NS asns1.customer.ne.jp.
csmaildealer.com. 5 NS asns2.customer.ne.jp.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0