www.siel.serv.si has no MX records.
Question and response
Question
dig www.siel.serv.si. MX
Answer
The response has no answer records.
Authority
serv.si. 1800 SOA dns1.siel.si. dns.siel.si. 2742 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0