Apex domains cannot have CNAME records.
Question and response
Question
dig smtt.ro. NS
Answer
smtt.ro. 4 NS ns2-09.azure-dns.net.
smtt.ro. 4 NS ns4-09.azure-dns.info.
smtt.ro. 4 NS ns1-09.azure-dns.com.
smtt.ro. 4 NS ns3-09.azure-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0