ns4.tbh.net has no MX records.
Question and response
Question
dig ns4.tbh.net. MX
Answer
The response has no answer records.
Authority
tbh.net. 3600 SOA ns3.tbh.net. help.tbh.net. 2025091006 3600 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0