here is an example:

        devShells.default = (pkgs.mkShell.override { stdenv = stdenv';}) {
          nativeBuildInputs = buildDevToolsDeps ++ buildToolsDeps ++ shellTools;
          buildInputs = buildDeps ++ testDeps;
          shellHook =
            ''
              BUILDER= ZDOTDIR=${zshDir} zsh -d && exit
            '';
        };

        # This shell is gcc based and we use it only
        # for the mathematics side of our design
        devShells.math = nativePkgs.mkShell {
          #nativeBuildInputs = mathDeps;
          buildInputs = mathDeps;
          shellHook =
            ''
              BUILDER=Math ZDOTDIR=${zshDir} zsh -d && exit
            '';
        };

In reply to @netpleb:matrix.org
and if I do not get the infinit recursion error, then I get an error "the option containers.mycontainername.mailserver" does not exist. There must be some trick I am missing.

In reply to @buckley310:matrix.org
hard to say without seeing the config. I do have a working mailserver using that project though, so if you can show how you're setting it up I can compare