POP3协议中的RETR命令为何不能显示邮件的内容？

如题，先谢谢各位。。。
主要代码如下：

private TcpClient mailclient;
private NetworkStream ns;
private StreamReader sr;
private StreamWriter sw;

sw.WriteLine("Stat");//执行pop3权限检查命令
sw.Flush();
m_response = sr.ReadLine();
string[] nummess = m_response.Split(' ');
totmessages = Convert.ToInt16(nummess[1]);//获取服务器中有几封信件
if (totmessages > 0)
{
this.L_Conut.Text = "you have " + totmessages + " messages";
}
else
{
this.L_Conut.Text = "you have no messages";
}
sw.WriteLine("retr 1");
sw.Flush();
m_response = Convert.ToString(sr.ReadLine());
this.Tb_Body.Text = m_response;