smtp4.tripnet.se has no MX records.
Question and response
Question
dig smtp4.tripnet.se. MX
Answer
The response has no answer records.
Authority
tripnet.se. 900 SOA ns0.tripnet.se. hostmaster.tripnet.se. 43638 7200 720 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0