_spf.smtp.leidenuniv.nl has no NS records.
NS records for this zone are defined at leidenuniv.nl.
NS records for this zone are defined at leidenuniv.nl.
Question and response
Question
dig _spf.smtp.leidenuniv.nl. NS
Answer
The response has no answer records.
Authority
leidenuniv.nl. 7200 SOA arachne.leidenuniv.nl. postmaster.leidenuniv.nl. 2006744200 10800 1080 2592000 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0