mxin.case.sfr.fr has no CNAME records.
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 1232, xrcode 0, version 0, flags 0