Apex domains cannot have CNAME records.
Question and response
Question
dig rackhostmx.com. NS
Answer
rackhostmx.com. 5 NS ns1.dns24.hu.
rackhostmx.com. 5 NS ns3.dns24.hu.
rackhostmx.com. 5 NS ns2.dns24.hu.
rackhostmx.com. 5 NS ns4.dns24.hu.
Authority
The response has no authority records.
Additional
ns1.dns24.hu. 5 A 91.227.139.139
ns2.dns24.hu. 5 A 87.229.26.40
ns3.dns24.hu. 5 A 185.80.50.47
ns4.dns24.hu. 5 A 79.139.57.64
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0