First try to install Stalwart as a mail software

flake-module.nix

@@ -53,6 +53,12 @@
     _module.args.pkgs = import inputs.nixpkgs {
       inherit system;
       config.permittedInsecurePackages = ["jitsi-meet-1.0.8043"];
+
+      overlays = [
+        (_: _: {
+          alias-to-sieve = inputs.alias-to-sieve.packages.x86_64-linux.default; # add custom package to convert alias files to sieve scripts on the stalwart machine
+        })
+      ];
     };
   };