Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.ap-northeast-2.amazonses.com. NS
Answer
smtp-out.ap-northeast-2.amazonses.com. 2 NS ns-215.awsdns-26.com.
smtp-out.ap-northeast-2.amazonses.com. 2 NS ns-1102.awsdns-09.org.
smtp-out.ap-northeast-2.amazonses.com. 2 NS ns-843.awsdns-41.net.
smtp-out.ap-northeast-2.amazonses.com. 2 NS ns-1605.awsdns-08.co.uk.
Authority
The response has no authority records.
Additional
ns-215.awsdns-26.com. 2 A 205.251.192.215
ns-843.awsdns-41.net. 2 A 205.251.195.75
ns-1102.awsdns-09.org. 2 A 205.251.196.78
ns-1605.awsdns-08.co.uk. 2 A 205.251.198.69
ns-215.awsdns-26.com. 2 AAAA 2600:9000:5300:d700:0:0:0:1
ns-843.awsdns-41.net. 2 AAAA 2600:9000:5303:4b00:0:0:0:1
ns-1102.awsdns-09.org. 2 AAAA 2600:9000:5304:4e00:0:0:0:1
ns-1605.awsdns-08.co.uk. 2 AAAA 2600:9000:5306:4500:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0