spf.bellmts.net has no MX records.
Question and response
Question
dig spf.bellmts.net. MX
Answer
The response has no answer records.
Authority
bellmts.net. 900 SOA dns1.mts.net. dnsadmin.bellmts.net. 94 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0