ip.tng.de has no MX records.
Question and response
Question
dig ip.tng.de. MX
Answer
The response has no answer records.
Authority
ip.tng.de. 3600 SOA rdns1.tng.de. dns.tng.de. 1 21600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0