Apex domains cannot have CNAME records.
Question and response
Question
dig mailendo.com. NS
Answer
mailendo.com. 5 NS ns-318.awsdns-39.com.
mailendo.com. 5 NS ns-1672.awsdns-17.co.uk.
mailendo.com. 5 NS ns-1310.awsdns-35.org.
mailendo.com. 5 NS ns-599.awsdns-10.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0