Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.us-west-2.amazonses.com. NS
Answer
smtp-out.us-west-2.amazonses.com. 5 NS ns-251.awsdns-31.com.
smtp-out.us-west-2.amazonses.com. 5 NS ns-1688.awsdns-19.co.uk.
smtp-out.us-west-2.amazonses.com. 5 NS ns-1460.awsdns-54.org.
smtp-out.us-west-2.amazonses.com. 5 NS ns-532.awsdns-02.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0