Apex domains cannot have CNAME records.
Question and response
Question
dig etrn.email. NS
Answer
etrn.email. 5 NS ns2.etrn.email.
etrn.email. 5 NS ns1.etrn.email.
etrn.email. 5 NS ns6.etrn.email.
etrn.email. 5 NS ns3.etrn.email.
etrn.email. 5 NS ns5.etrn.email.
etrn.email. 5 NS ns4.etrn.email.
etrn.email. 5 NS ns7.etrn.email.
Authority
The response has no authority records.
Additional
ns1.etrn.email. 5 A 204.62.28.253
ns2.etrn.email. 5 A 204.62.29.253
ns3.etrn.email. 5 A 204.62.30.253
ns4.etrn.email. 5 A 204.62.31.253
ns5.etrn.email. 5 A 45.56.69.153
ns6.etrn.email. 5 A 174.143.150.29
ns7.etrn.email. 5 A 178.79.145.131
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0