nnb.dnsnode.net has no MX records.
Question and response
Question
dig nnb.dnsnode.net. MX
Answer
The response has no answer records.
Authority
dnsnode.net. 3600 SOA nna.netnod.se. noc.netnod.se. 1771459231 7200 1800 604800 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0