212.231.66.in-addr.arpa has no MX records.
Question and response
Question
dig 212.231.66.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
212.231.66.in-addr.arpa. 3600 SOA dns1.firstlight.net. postmaster.no.email.please. 598392153 3600 600 2592000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0