Apex domains cannot have CNAME records.
Question and response
Question
dig porcupine-mail.com. NS
Answer
porcupine-mail.com. 5 NS ns-824.awsdns-39.net.
porcupine-mail.com. 5 NS ns-1725.awsdns-23.co.uk.
porcupine-mail.com. 5 NS ns-4.awsdns-00.com.
porcupine-mail.com. 5 NS ns-1420.awsdns-49.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0