nmx1.es.net has no CNAME records.
Question and response
Question
dig nmx1.es.net. NS
Answer
The response has no answer records.
Authority
es.net. 595 SOA ns1.es.net. hostmaster.es.net. 2026025314 3600 3600 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0