mx.t-one.net.cust.b.hostedemail.com has no MX records.
Question and response
Question
dig mx.t-one.net.cust.b.hostedemail.com. MX
Answer
The response has no answer records.
Authority
cust.b.hostedemail.com. 300 SOA ns1.mdnsservice.com. hostmaster.mdnsservice.com. 953732100 10001 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0