sns02.hkn.de has no MX records.
Question and response
Question
dig sns02.hkn.de. MX
Answer
The response has no answer records.
Authority
hkn.de. 300 SOA neos.hkn.de. hostmaster.hkn.de. 1771487296 28800 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0