_spf.questback.net has no MX records.
Question and response
Question
dig _spf.questback.net. MX
Answer
The response has no answer records.
Authority
questback.net. 3600 SOA ns1.dnshost.net. zonemaster.dnshost.net. 1705568482 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0