mx01.perfora.net has no NS records.
NS records for this zone are defined at perfora.net.
NS records for this zone are defined at perfora.net.
Question and response
Question
dig mx01.perfora.net. NS
Answer
The response has no answer records.
Authority
perfora.net. 600 SOA rns.ui-dns.de. dnsadmin.1und1.de. 2013099627 10800 3600 604800 600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0