mts15.smtp.dk has no MX records.
Question and response
Question
dig mts15.smtp.dk. MX
Answer
The response has no answer records.
Authority
smtp.dk. 300 SOA ns.dandomain.dk. hostmaster.dandomain.dk. 2025062501 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0