mail.i-web.ch has no CNAME records.
Question and response
Question
dig mail.i-web.ch. NS
Answer
The response has no answer records.
Authority
i-web.ch. 3053 SOA dns1.i-web.ch. hostmaster.i-web.ch. 2026030701 21600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0