The famous German DNS blackhole list Nix Spam ceases operation and will likely be shut down this year.
Read more on heise.de (in English).
Therefore support for this DNSBL will be removed in the next release of Aimy Captcha-Less Form Guard. We recommend to disable the "DNSBL Tests: Nix Spam" option right now as still using the DNSBL may introduce issues.
We will implement support for another DNSBL as a replacement for Nix Spam soon.