Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-out.ca-central-1.amazonses.com. NS
Answer
smtp-out.ca-central-1.amazonses.com. 5 NS ns-89.awsdns-11.com.
smtp-out.ca-central-1.amazonses.com. 5 NS ns-927.awsdns-51.net.
smtp-out.ca-central-1.amazonses.com. 5 NS ns-1407.awsdns-47.org.
smtp-out.ca-central-1.amazonses.com. 5 NS ns-1870.awsdns-41.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0