cm.cleanmail.ch has no CNAME records.
Question and response
Question
dig cm.cleanmail.ch. NS
Answer
The response has no answer records.
Authority
cleanmail.ch. 4709 SOA ns3.cleanmail.ch. hostmaster.cleanmail.ch. 2025121802 86400 7200 3600000 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0