8.66.216.in-addr.arpa has no MX records.
Question and response
Question
dig 8.66.216.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
8.66.216.in-addr.arpa. 86400 SOA ns1.he.net. hostmaster.he.net. 2026030700 10800 1800 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0