mail.hostxtrem.com has no CNAME records.
Question and response
Question
dig mail.hostxtrem.com. NS
Answer
The response has no answer records.
Authority
hostxtrem.com. 3341 SOA ns1.hostxtrem.com. alberto\.garcia.aow.es. 2026022405 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0