backend.antagus.de has no MX records.
Question and response
Question
dig backend.antagus.de. MX
Answer
The response has no answer records.
Authority
antagus.de. 3600 SOA ns1.antagus.de. root.ns1.antagus.de. 1692803702 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0