mx20.sunrise.net has no MX records.
Question and response
Question
dig mx20.sunrise.net. MX
Answer
The response has no answer records.
Authority
sunrise.net. 3600 SOA dns1.sunrise.ch. business-support.sunrise.net. 2026021708 28800 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0