nixos/msmtp: add package option

    programs.msmtp = {

      enable = lib.mkEnableOption "msmtp - an SMTP client";

      package = lib.mkPackageOption pkgs "msmtp" { };

      setSendmail = lib.mkOption {

        type = lib.types.bool;

        default = true;

  };

  config = lib.mkIf cfg.enable {

    environment.systemPackages = [ pkgs.msmtp ];

    environment.systemPackages = [ cfg.package ];

    services.mail.sendmailSetuidWrapper = lib.mkIf cfg.setSendmail {

      program = "sendmail";

      source = "${pkgs.msmtp}/bin/sendmail";

      source = "${cfg.package}/bin/sendmail";

      setuid = false;

      setgid = false;

      owner = "root";