one.one.one has no MX records.
Question and response
Question
dig one.one.one. MX
Answer
The response has no answer records.
Authority
one.one.one. 1800 SOA dorthy.ns.cloudflare.com. dns.cloudflare.com. 2396726445 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0