Apex domains cannot have CNAME records.
Question and response
Question
dig fra1.oracleemaildelivery.com. NS
Answer
fra1.oracleemaildelivery.com. 2 NS ns3.p01.dynect.net.
fra1.oracleemaildelivery.com. 2 NS ns1.p01.dynect.net.
fra1.oracleemaildelivery.com. 2 NS ns2.p01.dynect.net.
fra1.oracleemaildelivery.com. 2 NS ns4.p01.dynect.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0