Apex domains cannot have CNAME records.
Question and response
Question
dig SecureMessage.us. NS
Answer
securemessage.us. 3 NS dns1.cscdns.net.
securemessage.us. 3 NS dns2.cscdns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0