Apex domains cannot have CNAME records.
Question and response
Question
dig elasticemail.com. NS
Answer
elasticemail.com. 5 NS ns-776.awsdns-33.net.
elasticemail.com. 5 NS ns-1228.awsdns-25.org.
elasticemail.com. 5 NS ns-1687.awsdns-18.co.uk.
elasticemail.com. 5 NS ns-270.awsdns-33.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0