mail.chezaubert.net has no CNAME records.
Question and response
Question
dig mail.chezaubert.net. NS
Answer
The response has no answer records.
Authority
chezaubert.net. 1207 SOA magpie.chezaubert.net. jack.chezaubert.net. 1346 21600 1800 1814000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0