Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.eu-central-1.amazonses.com. NS
Answer
smtp-out.eu-central-1.amazonses.com. 5 NS ns-1087.awsdns-07.org.
smtp-out.eu-central-1.amazonses.com. 5 NS ns-1754.awsdns-27.co.uk.
smtp-out.eu-central-1.amazonses.com. 5 NS ns-174.awsdns-21.com.
smtp-out.eu-central-1.amazonses.com. 5 NS ns-540.awsdns-03.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0