_spf.sas.com has no NS records.
NS records for this zone are defined at sas.com.
NS records for this zone are defined at sas.com.
Question and response
Question
dig _spf.sas.com. NS
Answer
The response has no answer records.
Authority
sas.com. 600 SOA dns3axxD0101nc0.net.sas.com. dnsadmin.sas.com. 2078289166 1800 300 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0