Apex domains cannot have CNAME records.
Question and response
Question
dig turbo-smtp.com. NS
Answer
turbo-smtp.com. 4 NS ns2.softlayer.com.
turbo-smtp.com. 4 NS ns1.softlayer.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0