spf.vpls.com has no NS records.
NS records for this zone are defined at vpls.com.
NS records for this zone are defined at vpls.com.
Question and response
Question
dig spf.vpls.com. NS
Answer
The response has no answer records.
Authority
vpls.com. 1800 SOA chin.ns.cloudflare.com. dns.cloudflare.com. 2397469117 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0