cat.ns.nic.es has no MX records.
Question and response
Question
dig cat.ns.nic.es. MX
Answer
The response has no answer records.
Authority
nic.es. 7200 SOA ns1.nic.es. hostmaster.red.es. 2026020701 7200 1800 1209600 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0