Apex domains cannot have CNAME records.
Question and response
Question
dig postlook.org. NS
Answer
postlook.org. 5 NS ns-1651.awsdns-14.co.uk.
postlook.org. 5 NS ns-748.awsdns-29.net.
postlook.org. 5 NS ns-269.awsdns-33.com.
postlook.org. 5 NS ns-1189.awsdns-20.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0