mx.jon.cz has no NS records.
NS records for this zone are defined at jon.cz.
NS records for this zone are defined at jon.cz.
Question and response
Question
dig mx.jon.cz. NS
Answer
The response has no answer records.
Authority
jon.cz. 3600 SOA ns.dns4.cz. hostmaster.active24.cz. 2026012103 10800 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0