Apex domains cannot have CNAME records.
Question and response
Question
dig omail.cc. NS
Answer
omail.cc. 5 NS ns1.huaweicloud-dns.cn.
omail.cc. 5 NS ns1.huaweicloud-dns.com.
omail.cc. 5 NS ns1.huaweicloud-dns.net.
omail.cc. 5 NS ns1.huaweicloud-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0