customers.hiper-net.dk has no MX records.
Question and response
Question
dig customers.hiper-net.dk. MX
Answer
The response has no answer records.
Authority
customers.hiper-net.dk. 3600 SOA ns3.hiper.dk. root.hiper.dk. 1772851486 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0