mail.belurs.at has no MX records.
Question and response
Question
dig mail.belurs.at. MX
Answer
The response has no answer records.
Authority
at. 10800 SOA dns.nic.at. domain-admin.univie.ac.at. 1771736402 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0