136.78.5.clients.your-server.de has no MX records.
Question and response
Question
dig 136.78.5.clients.your-server.de. MX
Answer
The response has no answer records.
Authority
136.78.5.clients.your-server.de. 86400 SOA ns1.your-server.de. dns.hetzner.com. 2022013148 14400 1800 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0