spf.voipgateway.org has no MX records.
Question and response
Question
dig spf.voipgateway.org. MX
Answer
The response has no answer records.
Authority
voipgateway.org. 86400 SOA ns1.backbone.ch. hostmaster.backbone.ch. 2025112600 600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0