_spf-sfdc.successfactors.com has no NS records.
NS records for this zone are defined at successfactors.com.
NS records for this zone are defined at successfactors.com.
Question and response
Question
dig _spf-sfdc.successfactors.com. NS
Answer
The response has no answer records.
Authority
successfactors.com. 3600 SOA ns1.sap.net. dns.sap-ag.de. 1773673528 3578 3600 2592000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0