Apex domains cannot have CNAME records.
Question and response
Question
dig elasticemail.net. NS
Answer
elasticemail.net. 5 NS ns-1034.awsdns-01.org.
elasticemail.net. 5 NS ns-190.awsdns-23.com.
elasticemail.net. 5 NS ns-868.awsdns-44.net.
elasticemail.net. 5 NS ns-2015.awsdns-59.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0