using System;using System。Collections。Generic;using System。Net;using System。Net。Sockets;using System。Threading;using System。

Text;using System。IO;class Server{ Socket _listenSocket; Dictionary _clients; public Server(int port) { _clients = new Dictionary(); _listenSocket = new Socket(AddressFamily。

InterNetwork, SocketType。Stream, ProtocolType。Tcp); IPEndPoint lep = new IPEndPoint(IPAddress。Any, port); _listenSocket。

Bind(lep); } public void Start() { _listenSocket。Listen(5); for (; ; ) { Socket client = _listenSocket。

Accept(); ClientProcess cp = new ClientProcess(this, client); ThreadStart ts = new ThreadStart(cp。Process); Thread t = new Thread(ts); t。

Start(); } } public void AddClient(string email, ClientProcess c) { lock (_clients) { if (!_clients。

ContainsKey(email)) _clients。Add(email, c); } } public void RemoveClient(string email) { lock (_clients) { if (_clients。

ContainsKey(email)) _clients。Remove(email); } } public void SendTo(string from, string email, string msg) { ClientProcess cp; lock(_clients) { _clients。

TryGetValue(email, out cp); } if (cp != null) { cp。Send(from, msg); } }}class ClientProcess{ Server _serv; Socket _s; TcpClient _tc; StreamReader _sr; StreamWriter _sw; string email; public ClientProcess(Server serv, Socket s) { _serv = serv; _s = s; _tc = new TcpClient(); _tc。

Client = _s; _sr = new StreamReader(_tc。GetStream()); _sw = new StreamWriter(_tc。GetStream()); } public void Process() { try { email = _sr。

ReadLine(); _serv。AddClient(email, this); for (; ; ) { string l = _sr。ReadLine(); int i = l。

IndexOf(":"); if(i == -1) continue; string em = l。Substring(0, i); string msg = l。

Substring(i 1); _serv。SendTo(email, em, msg); } } catch { _serv。

RemoveClient(email); } } public void Send(string email, string msg) { _sw。WriteLine("{0}:{1}", email, msg); _sw。

Flush(); }}class Program{ static void Main(string[] args) { Server s = new Server(12345); s。Start(); }}協議是這樣的： 1、傳送和接收都是以行為單位的 2、客戶端連線後傳送的第一行資料是自己的郵箱 3、客戶端之後傳送的格式是： 對方郵箱 冒號 要傳送的訊息。

冒號是英文半形冒號，郵箱和冒號間沒有空格。