mx1.vtx.ch has no CNAME records.
Question and response
Question
dig mx1.vtx.ch. NS
Answer
The response has no answer records.
Authority
vtx.ch. 4690 SOA ns01.vtx.ch. dnsmaster.vtx.ch. 2026020205 21600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0