mail.contenuthemes.com has no CNAME records.
Question and response
Question
dig mail.contenuthemes.com. NS
Answer
The response has no answer records.
Authority
contenuthemes.com. 3157 SOA dns.contenuthemes.com. hostmaster.contenuthemes.com. 1895830550 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0