dns-backup.spanier.es has no MX records.
Question and response
Question
dig dns-backup.spanier.es. MX
Answer
The response has no answer records.
Authority
spanier.es. 300 SOA nox.spnr.de. hostmaster.spnr.de. 2035 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0