Apex domains cannot have CNAME records.
Question and response
Question
dig bluewin.org. NS
Answer
bluewin.org. 5 NS dns3.swisscom.com.
bluewin.org. 5 NS dns1.swisscom.com.
bluewin.org. 5 NS dns2.swisscom.com.
Authority
The response has no authority records.
Additional
dns1.swisscom.com. 5 A 138.190.34.196
dns2.swisscom.com. 5 A 138.190.34.204
dns3.swisscom.com. 5 A 193.222.76.54
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0