Apex domains cannot have CNAME records.
Question and response
Question
dig smmx.nifty.com. NS
Answer
smmx.nifty.com. 5 NS ns-1842.awsdns-38.co.uk.
smmx.nifty.com. 5 NS ns-945.awsdns-54.net.
smmx.nifty.com. 5 NS ns-436.awsdns-54.com.
smmx.nifty.com. 5 NS ns-1522.awsdns-62.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0