ns2.rbg.tum.de has no MX records.
Question and response
Question
dig ns2.rbg.tum.de. MX
Answer
The response has no answer records.
Authority
rbg.tum.de. 3600 SOA tuminfo1.rbg.tum.de. rbg-system.rbg.tum.de. 45822 86400 3600 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0