Apex domains cannot have CNAME records.
Question and response
Question
dig dkim.e2ma.net. NS
Answer
dkim.e2ma.net. 5 NS ns-1185.awsdns-20.org.
dkim.e2ma.net. 5 NS ns-1571.awsdns-04.co.uk.
dkim.e2ma.net. 5 NS ns-221.awsdns-27.com.
dkim.e2ma.net. 5 NS ns-752.awsdns-30.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0