Apex domains cannot have CNAME records.
Question and response
Question
dig mail.clinchtalent.com. NS
Answer
mail.clinchtalent.com. 5 NS ns-1069.awsdns-05.org.
mail.clinchtalent.com. 5 NS ns-1861.awsdns-40.co.uk.
mail.clinchtalent.com. 5 NS ns-268.awsdns-33.com.
mail.clinchtalent.com. 5 NS ns-601.awsdns-11.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0