mx.mail-pagedeslibraires.fr has no CNAME records.
Question and response
Question
dig mx.mail-pagedeslibraires.fr. NS
Answer
The response has no answer records.
Authority
mail-pagedeslibraires.fr. 3358 SOA a.dns.gandi.net. hostmaster.gandi.net. 1553874976 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0