mail01.iserver.si has no NS records.
NS records for this zone are defined at iserver.si.
NS records for this zone are defined at iserver.si.
Question and response
Question
dig mail01.iserver.si. NS
Answer
The response has no answer records.
Authority
iserver.si. 1800 SOA konnor.ns.cloudflare.com. dns.cloudflare.com. 2396400172 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0