_spf.tisf.net has no CNAME records.
Question and response
Question
dig _spf.tisf.net. NS
Answer
The response has no answer records.
Authority
tisf.net. 120 SOA jokulsa.asbyrgi.net. hostmaster.tisf.net. 2026022616 7200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0