smtp-b.netnod.se has no MX records.
Question and response
Question
dig smtp-b.netnod.se. MX
Answer
The response has no answer records.
Authority
netnod.se. 3600 SOA nna.netnod.se. noc.netnod.se. 1772064031 7200 1800 604800 7200
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0