Apex domains cannot have CNAME records.
Question and response
Question
dig rediffmailpro.com. NS
Answer
rediffmailpro.com. 5 NS use4.akam.net.
rediffmailpro.com. 5 NS use9.akam.net.
rediffmailpro.com. 5 NS ns1-245.akam.net.
rediffmailpro.com. 5 NS eur4.akam.net.
rediffmailpro.com. 5 NS usc2.akam.net.
rediffmailpro.com. 5 NS eur1.akam.net.
rediffmailpro.com. 5 NS asia2.akam.net.
rediffmailpro.com. 5 NS ns1-225.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0