mx.cetsi.fr has no MX records.
Question and response
Question
dig mx.cetsi.fr. MX
Answer
The response has no answer records.
Authority
cetsi.fr. 3600 SOA ns1.cetsi.fr. postmaster.cetsi.fr. 2016585338 21600 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0