Apex domains cannot have CNAME records.
Question and response
Question
dig responsys.net. NS
Answer
responsys.net. 3 NS a13-67.akam.net.
responsys.net. 3 NS a2-66.akam.net.
responsys.net. 3 NS a9-64.akam.net.
responsys.net. 3 NS a1-31.akam.net.
responsys.net. 3 NS a12-67.akam.net.
responsys.net. 3 NS a16-65.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0