mail.infomail.es has no CNAME records.
Question and response
Question
dig mail.infomail.es. NS
Answer
The response has no answer records.
Authority
infomail.es. 300 SOA nsjc8hos01.telefonica-data.com. dnsadmin.tsai.es. 2013042313 14400 7200 2592000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0