200.in-addr.arpa has no MX records.
Question and response
Question
dig 200.in-addr.arpa. MX
Answer
The response has no answer records.
Authority
200.in-addr.arpa. 10800 SOA ns.lacnic.net. hostmaster.lacnic.net. 2026032132 1800 900 691200 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0