dc.kpn.net has no MX records.
Question and response
Question
dig dc.kpn.net. MX
Answer
The response has no answer records.
Authority
dc.kpn.net. 3600 SOA ns7.kpn.net. zonemaster.kpn.com. 2020081801 900 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0