mx-clients.optimitel.fr has no CNAME records.
Question and response
Question
dig mx-clients.optimitel.fr. NS
Answer
The response has no answer records.
Authority
optimitel.fr. 866 SOA tic.ipnotic-telecom.fr. hostmaster.ipnotic-telecom.fr. 2021021801 10800 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0