Apex domains cannot have CNAME records.
Question and response
Question
dig realsender.com. NS
Answer
realsender.com. 5 NS ns-346.awsdns-43.com.
realsender.com. 5 NS ns-1002.awsdns-61.net.
realsender.com. 5 NS ns-1141.awsdns-14.org.
realsender.com. 5 NS ns-1745.awsdns-26.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0