mx.i.root-servers.org has no MX records.
Question and response
Question
dig mx.i.root-servers.org. MX
Answer
The response has no answer records.
Authority
i.root-servers.org. 3600 SOA nna.netnod.se. noc.netnod.se. 1771459205 7200 1800 604800 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0