_spf.hp.com has no NS records.
NS records for this zone are defined at hp.com.
NS records for this zone are defined at hp.com.
Question and response
Question
dig _spf.hp.com. NS
Answer
The response has no answer records.
Authority
hp.com. 900 SOA txa01hpiibpe.ams.hp.net. hostmaster.hp.com. 443247649 3600 3600 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0