mx2.relay.renater.fr has no CNAME records.
Question and response
Question
dig mx2.relay.renater.fr. NS
Answer
The response has no answer records.
Authority
relay.renater.fr. 10800 SOA ns1.renater.fr. admins.renater.fr. 2015091909 21600 3600 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0