Apex domains cannot have CNAME records.
Question and response
Question
dig mailerxses.com. NS
Answer
mailerxses.com. 5 NS ns-34.awsdns-04.com.
mailerxses.com. 5 NS ns-1407.awsdns-47.org.
mailerxses.com. 5 NS ns-964.awsdns-56.net.
mailerxses.com. 5 NS ns-1852.awsdns-39.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0