_spf.iis.se has no MX records.
Question and response
Question
dig _spf.iis.se. MX
Answer
The response has no answer records.
Authority
iis.se. 480 SOA nsa.dnsnode.net. hostmaster.nic.se. 1772630093 14400 3600 2592000 480
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0