nixos/modules/hardware/drive-monitor/default.nix

{ config, lib, pkgs, ... }:
let
  cfg = config.my.hardware.drive-monitor;
in
{
  options.my.hardware.drive-monitor = with lib; {
    enable = mkEnableOption "drive-monitor configuration";

    OnFailureMail = mkOption {
      type = types.nullOr (types.str);
      description = lib.mdDoc "Mail adress where to send the error report";
      default = null;
      example = "alarm@mail.com";
    };
  };

  config = lib.mkIf cfg.enable {
    services = {
      postfix.enable = lib.mkIf (cfg.OnFailureMail != null) true;
      smartd = {
        enable = true;
        notifications.mail = lib.mkIf (cfg.OnFailureMail != null) {
          enable = true;
          recipient = cfg.OnFailureMail;
        };
      };
    };
  };
}