mx.one.com has no MX records.
Question and response
Question
dig mx.one.com. MX
Answer
The response has no answer records.
Authority
mx.one.com. 600 SOA service.g1-dns.one. hostmaster.group.one. 2025051408 14400 3600 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0