mx2.swisslink.ch has no CNAME records.
Question and response
Question
dig mx2.swisslink.ch. NS
Answer
The response has no answer records.
Authority
swisslink.ch. 10489 SOA ns1.swisslink.ch. dnsmaster.swisslink.ch. 2026022406 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0