mailserver.martinahautau.de has no MX records.
Question and response
Question
dig mailserver.martinahautau.de. MX
Answer
The response has no answer records.
Authority
martinahautau.de. 7200 SOA ns5.kasserver.com. hostmaster.kasserver.com. 2509051103 28800 7200 1209600 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0