Apex domains cannot have CNAME records.
Question and response
Question
dig mtaspm.email. NS
Answer
mtaspm.email. 5 NS ns-1814.awsdns-34.co.uk.
mtaspm.email. 5 NS ns-1260.awsdns-29.org.
mtaspm.email. 5 NS ns-23.awsdns-02.com.
mtaspm.email. 5 NS ns-576.awsdns-08.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0