Apex domains cannot have CNAME records.
Question and response
Question
dig rs101-realsender.com. NS
Answer
rs101-realsender.com. 5 NS ns-1283.awsdns-32.org.
rs101-realsender.com. 5 NS ns-989.awsdns-59.net.
rs101-realsender.com. 5 NS ns-34.awsdns-04.com.
rs101-realsender.com. 5 NS ns-1753.awsdns-27.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0