Apex domains cannot have CNAME records.
Question and response
Question
dig xsend4.email. NS
Answer
xsend4.email. 4 NS ns-1978.awsdns-55.co.uk.
xsend4.email. 4 NS ns-1137.awsdns-14.org.
xsend4.email. 4 NS ns-65.awsdns-08.com.
xsend4.email. 4 NS ns-853.awsdns-42.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0