mx.inext.cz has no CNAME records.
Question and response
Question
dig mx.inext.cz. NS
Answer
The response has no answer records.
Authority
inext.cz. 3600 SOA ns1.inext.cz. hostmaster.inext.cz. 2023101289 3600 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0