smtp01.net.sigma.se has no MX records.
Question and response
Question
dig smtp01.net.sigma.se. MX
Answer
The response has no answer records.
Authority
net.sigma.se. 86400 SOA ns01.mgmt.rts.se. hostmaster.sigma.se. 2023032101 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0