backup-server.nordu.net has no MX records.
Question and response
Question
dig backup-server.nordu.net. MX
Answer
The response has no answer records.
Authority
nordu.net. 300 SOA hidden-master.nordu.net. hostmaster.nordu.net. 2026021803 14400 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0