Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.eu-north-1.amazonses.com. NS
Answer
smtp-out.eu-north-1.amazonses.com. 5 NS ns-559.awsdns-05.net.
smtp-out.eu-north-1.amazonses.com. 5 NS ns-1736.awsdns-25.co.uk.
smtp-out.eu-north-1.amazonses.com. 5 NS ns-444.awsdns-55.com.
smtp-out.eu-north-1.amazonses.com. 5 NS ns-1288.awsdns-33.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0