ns01.one.com has no MX records.
Question and response
Question
dig ns01.one.com. MX
Answer
The response has no answer records.
Authority
one.com. 300 SOA a.b-one-dns.net. hostmaster.one.com. 2026021901 1800 900 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0