ruhr has no MX records.
Question and response
Question
dig ruhr. MX
Answer
The response has no answer records.
Authority
ruhr. 900 SOA ns0.centralnic.net. hostmaster.centralnic.net. 2209135492 900 1800 6048000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0