mx.ireo-perigord.com has no CNAME records.
Question and response
Question
dig mx.ireo-perigord.com. NS
Answer
The response has no answer records.
Authority
ireo-perigord.com. 1862 SOA dns.ireo-perigord.com. hostmaster.ireo-perigord.com. 1438168773 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0