{
  description = "SMTP forwarding relay daemon with signing and encryption";

  inputs = {
    nixpkgs.url = "nixpkgs/nixpkgs-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs =
    { self
    , nixpkgs
    , flake-utils
    ,
    }:
    let
      supportedSystems = [
        "x86_64-linux"
        "aarch64-darwin"
      ];
    in
    {
      overlays.default = import ./overlay.nix { inherit self; };
    }
    // flake-utils.lib.eachSystem supportedSystems (
      system:
      let
        pkgs = import nixpkgs { inherit system; };
      in
      {
        packages = {
          smtprd-ng = pkgs.callPackage ./. { };
        };

        packages.default = self.packages.${system}.smtprd-ng;

        apps.default = {
          type = "app";
          program = "${self.packages.${system}.smtprd-ng}/bin/smtprd-ng";
        };
      }
    );
}