mx01.dialtelecom.cz has no CNAME records.
Question and response
Question
dig mx01.dialtelecom.cz. NS
Answer
The response has no answer records.
Authority
dialtelecom.cz. 3600 SOA names.dialtelecom.cz. hostmaster.dialtelecom.cz. 2026022522 600 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0