spf.zixsmbhosted.com has no MX records.
Question and response
Question
dig spf.zixsmbhosted.com. MX
Answer
The response has no answer records.
Authority
zixsmbhosted.com. 600 SOA ns.zixcorp.com. noc.zixcorp.com. 2025081101 3600 300 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0