Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.eu-west-1.amazonses.com. NS
Answer
smtp-out.eu-west-1.amazonses.com. 5 NS ns-133.awsdns-16.com.
smtp-out.eu-west-1.amazonses.com. 5 NS ns-1353.awsdns-41.org.
smtp-out.eu-west-1.amazonses.com. 5 NS ns-869.awsdns-44.net.
smtp-out.eu-west-1.amazonses.com. 5 NS ns-1802.awsdns-33.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0