iana-servers.net has no MX records.
Question and response
Question
dig iana-servers.net. MX
Answer
The response has no answer records.
Authority
iana-servers.net. 3600 SOA sns.dns.icann.org. noc.dns.icann.org. 2022092664 10800 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0