posta.dobnet.cz has no CNAME records.
Question and response
Question
dig posta.dobnet.cz. NS
Answer
The response has no answer records.
Authority
dobnet.cz. 7200 SOA ns1.dobnet.cz. service.dobnet.cz. 2026022302 3600 900 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0