Apex domains cannot have CNAME records.
Question and response
Question
dig referral-mail.com. NS
Answer
referral-mail.com. 5 NS ns-1597.awsdns-07.co.uk.
referral-mail.com. 5 NS ns-1424.awsdns-50.org.
referral-mail.com. 5 NS ns-188.awsdns-23.com.
referral-mail.com. 5 NS ns-572.awsdns-07.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0