Apex domains cannot have CNAME records.
Question and response
Question
dig ssmx.net. NS
Answer
ssmx.net. 5 NS rose.ns.cloudflare.com.
ssmx.net. 5 NS igor.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0