mail4.itu.ch has no CNAME records.
Question and response
Question
dig mail4.itu.ch. NS
Answer
The response has no answer records.
Authority
itu.ch. 542 SOA ns.itu.ch. hostmaster.itu.ch. 2026030901 1800 900 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0