spf.verizonwireless.com has no MX records.
Question and response
Question
dig spf.verizonwireless.com. MX
Answer
The response has no answer records.
Authority
verizonwireless.com. 900 SOA ns-twbg.verizonwireless.com. dnsadmin.verizonwireless.com. 25718 1800 600 604800 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0