dns3.swisscom.com has no MX records.
Question and response
Question
dig dns3.swisscom.com. MX
Answer
The response has no answer records.
Authority
swisscom.com. 600 SOA dns3.swisscom.com. admin\.dns.swisscom.com. 53605 21600 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0