Apex domains cannot have CNAME records.
Question and response
Question
dig cpmails.com. NS
Answer
cpmails.com. 5 NS ns-496.awsdns-62.com.
cpmails.com. 5 NS ns-1976.awsdns-55.co.uk.
cpmails.com. 5 NS ns-1493.awsdns-58.org.
cpmails.com. 5 NS ns-540.awsdns-03.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0