_spf.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 _spf.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