mail.plateau.com has no CNAME records.
Question and response
Question
dig mail.plateau.com. NS
Answer
The response has no answer records.
Authority
plateau.com. 844 SOA ns1.sap.net. dns.sap-ag.de. 1772071263 3590 86400 2592000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0