mail.combell.com has no CNAME records.
Question and response
Question
dig mail.combell.com. NS
Answer
The response has no answer records.
Authority
combell.com. 3600 SOA ns3.combell.net. hostmaster.combell.com. 1766403047 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0