mail.barbuchu.com has no CNAME records.
Question and response
Question
dig mail.barbuchu.com. NS
Answer
The response has no answer records.
Authority
barbuchu.com. 600 SOA ns1.la-boite.com. admin.la-boite.com. 2026020303 3600 600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0