ns3.interdomain.es has no MX records.
Question and response
Question
dig ns3.interdomain.es. MX
Answer
The response has no answer records.
Authority
interdomain.es. 300 SOA ns1.interdomain.net. admin.interdomain.net. 703853900 28800 7200 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0