prisoner.iana.org has no MX records.
Question and response
Question
dig prisoner.iana.org. MX
Answer
The response has no answer records.
Authority
iana.org. 3600 SOA sns.dns.icann.org. noc.dns.icann.org. 2025121345 7200 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0