Delphi-PRAXiS - Delphi kann mit idTCPServer / -Client nicht außerhalb von LANs send

Hab mit der Indy10-komponente TidTCPClient (und tidTCPServer) nen kleines "ChatProgramm" (also orlage für andere programme) geschrieben und kann damit auch strings innerhalb eines LAns verschicken.... aber leider nicht übers "interet"... wieso?

Delphi-Quellcode:

			unit Unit1;

interface

uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, idContext, StdCtrls, IdCustomTCPServer, IdTCPServer, IdBaseComponent,

  IdComponent, IdTCPConnection, IdTCPClient;

type

  TForm1 = class(TForm)

    IdTCPClient1: TIdTCPClient;

    IdTCPServer1: TIdTCPServer;

    Edit1: TEdit;

    Edit2: TEdit;

    Label1: TLabel;

    Label2: TLabel;

    Edit3: TEdit;

    Button2: TButton;

    Label3: TLabel;

    ListBox1: TListBox;

    Edit4: TEdit;

    Button1: TButton;

    procedure Button1Click(Sender: TObject);

    procedure IdTCPServer1Execute(AContext: TIdContext);

    procedure Button2Click(Sender: TObject);

    procedure FormCreate(Sender: TObject);

  private

    { Private-Deklarationen }

  public

    { Public-Deklarationen }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);

begin

IdTCPServer1.Active:= False;

IdTCPServer1.DefaultPort:=StrToInt(Edit4.Text);

IdTCPServer1.Active:= True;

end;

procedure TForm1.Button2Click(Sender: TObject);

begin

  with IdTCPClient1 do

    try

      Host := Edit1.Text;;

      Port := StrToInt(Edit2.Text);    

      Connect;

      ShowMessage('Connected.');

      try

        IdTCPClient1.IOHandler.WriteLn(Edit3.Text);

        ShowMessage('Gesendet.');

      finally

      Disconnect;

      ShowMessage('Disconnected.');

      end;

    finally

    end;

end;

procedure TForm1.IdTCPServer1Execute(AContext: TIdContext);

begin

ListBox1.Items.Add(AContext.Connection.IOHandler.ReadLn);

end;