mxbackup2.sbservers.cz has no NS records.
NS records for this zone are defined at sbservers.cz.
NS records for this zone are defined at sbservers.cz.
Question and response
Question
dig mxbackup2.sbservers.cz. NS
Answer
The response has no answer records.
Authority
sbservers.cz. 1800 SOA darwin.ns.cloudflare.com. dns.cloudflare.com. 2397466684 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0