user.ono.com has no MX records.
Question and response
Question
dig user.ono.com. MX
Answer
The response has no answer records.
Authority
user.ono.com. 3600 SOA dns01.ono.com. administrador.ono.es. 2023041101 3600 7200 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0