216.106.0.128.reverse.socket.net has no MX records.
Question and response
Question
dig 216.106.0.128.reverse.socket.net. MX
Answer
The response has no answer records.
Authority
reverse.socket.net. 43200 SOA ns1.socket.net. dns.socket.net. 2017081701 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0