217.0.81.in-addr.arpa has no MX records.
Question and response
Question
dig 217.0.81.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
217.0.81.in-addr.arpa. 10800 SOA ns1.casablanca.cz. servis.casablanca.cz. 2017032000 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0