mx.web4u.cz has no NS records.
NS records for this zone are defined at web4u.cz.
NS records for this zone are defined at web4u.cz.
Question and response
Question
dig mx.web4u.cz. NS
Answer
The response has no answer records.
Authority
web4u.cz. 60 SOA ns.web4u.cz. admin.web4u.cz. 2026021711 14400 3600 1209600 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0