166.216.65.in-addr.arpa has no MX records.
Question and response
Question
dig 166.216.65.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
166.216.65.in-addr.arpa. 21600 SOA auth00.ns.uu.net. hostmaster.UU.NET. 11 21600 3600 1728000 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0