mail.zonnet.net has no NS records.
NS records for this zone are defined at zonnet.net.
NS records for this zone are defined at zonnet.net.
Question and response
Question
dig mail.zonnet.net. NS
Answer
The response has no answer records.
Authority
zonnet.net. 86400 SOA ns.zonnet.nl. hostmaster.zonnet.nl. 2020083100 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0