sub192.55.136.210.in-addr.arpa has no MX records.
Question and response
Question
dig sub192.55.136.210.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
sub192.55.136.210.in-addr.arpa. 2560 SOA ns.jp.betrend.com. bt_mis.betrend.com. 1772005205 16384 2048 1048576 2560
Additional
The response has no additional records.