a.ip6-servers.arpa has no MX records.
Question and response
Question
dig a.ip6-servers.arpa. MX
Answer
The response has no answer records.
Authority
ip6-servers.arpa. 3600 SOA a.ip6-servers.arpa. nstld.iana.org. 2025071007 14400 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0