Apex domains cannot have CNAME records.
Question and response
Question
dig nico.email. NS
Answer
nico.email. 5 NS ns-601.awsdns-11.net.
nico.email. 5 NS ns-157.awsdns-19.com.
nico.email. 5 NS ns-1975.awsdns-54.co.uk.
nico.email. 5 NS ns-1262.awsdns-29.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0