spf1.exoscale.com has no NS records.
NS records for this zone are defined at exoscale.com.
NS records for this zone are defined at exoscale.com.
Question and response
Question
dig spf1.exoscale.com. NS
Answer
The response has no answer records.
Authority
exoscale.com. 3600 SOA ns1.exoscale.io. admin.dnsimple.com. 1518553153 86400 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0