Apex domains cannot have CNAME records.
Question and response
Question
dig unifiedpost.com. NS
Answer
unifiedpost.com. 5 NS public-ns3.unifiedpost.com.
unifiedpost.com. 5 NS public-ns2.unifiedpost.com.
unifiedpost.com. 5 NS public-ns1.unifiedpost.com.
Authority
The response has no authority records.
Additional
public-ns1.unifiedpost.com. 5 A 188.64.79.121
public-ns2.unifiedpost.com. 5 A 34.90.117.43
public-ns3.unifiedpost.com. 5 A 34.79.211.159
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0