Apex domains cannot have CNAME records.
Question and response
Question
dig on.themailspec.com. NS
Answer
on.themailspec.com. 4 NS pns3.cloud.sg.
on.themailspec.com. 4 NS pns4.cloud.sg.
on.themailspec.com. 4 NS pns1.cloud.sg.
on.themailspec.com. 4 NS pns2.cloud.sg.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0