ch.pro.io has no MX records.
Question and response
Question
dig ch.pro.io. MX
Answer
The response has no answer records.
Authority
pro.io. 86400 SOA ch.pro.io. dns.metanet.ch. 2017030715 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0