Apex domains cannot have CNAME records.
Question and response
Question
dig emservice.cz. NS
Answer
emservice.cz. 5 NS ns-1545.awsdns-01.co.uk.
emservice.cz. 5 NS ns-653.awsdns-17.net.
emservice.cz. 5 NS ns-359.awsdns-44.com.
emservice.cz. 5 NS ns-1478.awsdns-56.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0