smtp.combellgroup.com has no MX records.
Question and response
Question
dig smtp.combellgroup.com. MX
Answer
The response has no answer records.
Authority
combellgroup.com. 3600 SOA ns3.combell.net. hostmaster.combellgroup.com. 1754777819 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0