mails.seonet.cz has no NS records.
NS records for this zone are defined at seonet.cz.
NS records for this zone are defined at seonet.cz.
Question and response
Question
dig mails.seonet.cz. NS
Answer
The response has no answer records.
Authority
seonet.cz. 3600 SOA 1.ns.gigaserver.cz. dns.gigaserver.cz. 1545516517 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0