sigma1.postal.cyso.net has no NS records.
NS records for this zone are defined at postal.cyso.net.
NS records for this zone are defined at postal.cyso.net.
Question and response
Question
dig sigma1.postal.cyso.net. NS
Answer
The response has no answer records.
Authority
postal.cyso.net. 300 SOA ns1.cyso.nl. dnsadmin.cysonet.com. 1773273600 16384 2048 1048576 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0