mxin.case.sfr.fr has no NS records.
NS records for this zone are defined at case.sfr.fr.
NS records for this zone are defined at case.sfr.fr.
Question and response
Question
dig mxin.case.sfr.fr. NS
Answer
The response has no answer records.
Authority
case.sfr.fr. 900 SOA pranspub03.phys.prod. support.dns.sfr.net. 2013010207 3600 900 2419200 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0