spf.izonesoftware.com has no MX records.
Question and response
Question
dig spf.izonesoftware.com. MX
Answer
The response has no answer records.
Authority
izonesoftware.com. 1800 SOA igor.ns.cloudflare.com. dns.cloudflare.com. 2398280479 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0