spf.flexmail.net has no NS records.
NS records for this zone are defined at flexmail.net.
NS records for this zone are defined at flexmail.net.
Question and response
Question
dig spf.flexmail.net. NS
Answer
The response has no answer records.
Authority
flexmail.net. 3600 SOA ns3.combell.net. hostmaster.flexmail.net. 1764922866 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0