178.in-addr.arpa has no MX records.
Question and response
Question
dig 178.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
178.in-addr.arpa. 3600 SOA pri.authdns.ripe.net. dns.ripe.net. 1771615196 3600 600 864000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0