_spf.imperial.ac.uk has no NS records.
NS records for this zone are defined at ac.uk.
NS records for this zone are defined at ac.uk.
Question and response
Question
dig _spf.imperial.ac.uk. NS
Answer
The response has no answer records.
Authority
imperial.ac.uk. 3536 SOA ns0.imperial.ac.uk. hostmaster.imperial.ac.uk. 2025812646 2700 1800 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0