mx.cetsi.fr has no NS records.
NS records for this zone are defined at cetsi.fr.
NS records for this zone are defined at cetsi.fr.
Question and response
Question
dig mx.cetsi.fr. NS
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