mail.xeolis.com has no CNAME records.
Question and response
Question
dig mail.xeolis.com. NS
Answer
The response has no answer records.
Authority
xeolis.com. 291 SOA dns102.ovh.net. tech.ovh.net. 2026020900 86400 3600 3600000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0