rbgstmk.at has no MX records.
Question and response
Question
dig rbgstmk.at. MX
Answer
The response has no answer records.
Authority
rbgstmk.at. 900 SOA dns1.grz.at. hostmaster.rrz.co.at. 34 1800 600 1209600 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0