Apex domains cannot have CNAME records.
Question and response
Question
dig taximail.com. NS
Answer
taximail.com. 5 NS ns-792.awsdns-35.net.
taximail.com. 5 NS ns-271.awsdns-33.com.
taximail.com. 5 NS ns-1701.awsdns-20.co.uk.
taximail.com. 5 NS ns-1225.awsdns-25.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0