mail4.wnfnet.com has no MX records.
Question and response
Question
dig mail4.wnfnet.com. MX
Answer
The response has no answer records.
Authority
wnfnet.com. 86400 SOA ns1.markmonitor.com. hostmaster.markmonitor.com. 2025120102 86400 3600 2592000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0