backup.mx.spoje.net has no MX records.
Question and response
Question
dig backup.mx.spoje.net. MX
Answer
The response has no answer records.
Authority
mx.spoje.net. 1800 SOA ns.spoje.net. tech.spoje.net. 1771956156 1800 3600 604800 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0