mx01.quantcom.cz has no CNAME records.
Question and response
Question
dig mx01.quantcom.cz. NS
Answer
The response has no answer records.
Authority
quantcom.cz. 3277 SOA names.dialtelecom.cz. hostmaster.dialtelecom.cz. 2026022206 21600 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0