mx.mailprotect.be has no CNAME records.
Question and response
Question
dig mx.mailprotect.be. NS
Answer
The response has no answer records.
Authority
mailprotect.be. 3600 SOA ns3.combell.net. hostmaster.mailprotect.be. 1764581328 10800 3600 604800 40000
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0