ns2.link11.de has no MX records.
Question and response
Question
dig ns2.link11.de. MX
Answer
The response has no answer records.
Authority
link11.de. 900 SOA ns1.link11.de. hostmaster.link11.de. 1771574236 16384 2048 1048576 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0