_spf.spnr.de has no NS records.
NS records for this zone are defined at spnr.de.
NS records for this zone are defined at spnr.de.
Question and response
Question
dig _spf.spnr.de. NS
Answer
The response has no answer records.
Authority
spnr.de. 300 SOA nox.spnr.de. hostmaster.spnr.de. 12989 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0