mail.dragonet.es has no CNAME records.
Question and response
Question
dig mail.dragonet.es. NS
Answer
The response has no answer records.
Authority
dragonet.es. 10288 SOA dns1.dragonet.es. admin.dragonet.es. 2003102001 86400 7200 2592000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0