mx.mailbox.orange-business.com has no CNAME records.
Question and response
Question
dig mx.mailbox.orange-business.com. NS
Answer
The response has no answer records.
Authority
orange-business.com. 3600 SOA dns1.equant.net. dns\.operations.orange.com. 2017022844 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0