mx.rezaxess.fr has no CNAME records.
Question and response
Question
dig mx.rezaxess.fr. NS
Answer
The response has no answer records.
Authority
rezaxess.fr. 3118 SOA ns1.rezaxess.fr. root.rezaxess.fr. 2018041201 43200 7200 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0