procedure TForm1.Button1Click(Sender: TObject);
var
  params: TStringList;
  request, content, response: string;
begin
  IdHTTP1.request.Charset := 'utf-8';
  IdHTTP1.request.BasicAuthentication := true;
  IdHTTP1.request.Username := 'User';
  IdHTTP1.request.Password := 'Passwort';
  IdHTTP1.request.ContentType := 'application/x-www-form-urlencoded';
  IdHTTP1.request.Host := '192.168.0.251:9876';

  params := TStringList.Create;
  try
    params.Add('type=fms');
    params.Add('address='+Edit1.Text);
    params.Add('status='+Edit2.Text);
    params.Add('message='+Memo1.Text);
    params.Add('info='+Edit3.Text);


    response := IdHTTP1.Post('http://192.168.0.251:9876/telegramin/alarmgeber/input.xml', params); // Hier ist der POST-Request
  finally
    params.Free;
  end;
end;