Apex domains cannot have CNAME records.
Question and response
Question
dig smartrecruiters.com. NS
Answer
smartrecruiters.com. 5 NS ns-770.awsdns-32.net.
smartrecruiters.com. 5 NS ns-1909.awsdns-46.co.uk.
smartrecruiters.com. 5 NS ns-216.awsdns-27.com.
smartrecruiters.com. 5 NS ns-1508.awsdns-60.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0