求用java Socket API编写一个SMTP邮件服务器程序

awdsdsds 的回答虽然不对题，不过也差不多了，说实话，我讨厌直接要结果的人。但是也许你是希望自己学到解决方式的人，所以给你个方式。
awdsdsds 建立的是个客户端，这里跑题了，你要自己做就得建立服务器。
ServerSocket 建立的时候注意一下端口就行了。不过也不是一定的，取决于你将来的客户端设置。

然后就accept()
等着对方创建连接吧。

然后就是数据格式的问题了。
你可以正常的用客户端发送一个最简单的分析一下数据格式，接来的肯定是字节，注意一下高低位。看看应该怎么将字节数据还原成邮件。

import Java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

public class SMTPDemo {

public static void main(String args[]) throws IOException,
UnknownHostException {
String msgFile = "file.txt";
String from = "java2s@java2s.com";
String to = "yourEmail@yourServer.com";
String mailHost = "yourHost";
SMTP mail = new SMTP(mailHost);
if (mail != null) {
if (mail.send(new FileReader(msgFile), from, to)) {
System.out.println("Mail sent.");
} else {
System.out.println("Connect to SMTP server failed!");
}
}
System.out.println("Done.");
}

static class SMTP {
private final static int SMTP_PORT = 25;

InetAddress mailHost;

InetAddress localhost;

BufferedReader in;

PrintWriter out;

public SMTP(String host) throws UnknownHostException {
mailHost = InetAddress.getByName(host);
localhost = InetAddress.getLocalHost();
System.out.println("mailhost = " + mailHost);
System.out.println("localhost= " + localhost);
System.out.println("SMTP constrUCtor done\n");
}

public boolean send(FileReader msgFileReader, String from, String to)
throws IOException {
Socket smtpPipe;
InputStream inn;
OutputStream outt;
BufferedReader msg;
msg = new BufferedReader(msgFileReader);
smtpPipe = new Socket(mailHost, SMTP_PORT);
if (smtpPipe == null) {
return false;
}
inn = smtpPipe.getInputStream();
outt = smtpPipe.getOutputStream();
in = new BufferedReader(new InputStreamReader(inn));
out = new PrintWriter(new OutputStreamWriter(outt), true);
if (inn == null outt == null) {
System.out.println("Failed to open streams to socket.");
return false;
}
String initialID = in.readLine();
System.out.println(initialID);
System.out.println("HELO " + localhost.getHostName());
out.println("HELO " + localhost.getHostName());
String welcome = in.readLine();
System.out.println(welcome);
System.out.println("MAIL From:<" + from + ">");
out.println("MAIL From:<" + from + ">");
String senderOK = in.readLine();
System.out.println(senderOK);
System.out.println("RCPT TO:<" + to + ">");
out.println("RCPT TO:<" + to + ">");
String recipientOK = in.readLine();
System.out.println(recipientOK);
System.out.println("DATA");
out.println("DATA");
String line;
while ((line = msg.readLine()) != null) {
out.println(line);
}
System.out.println(".");
out.println(".");
String acceptedOK = in.readLine();
System.out.println(acceptedOK);
System.out.println("QUIT");
out.println("QUIT");
return true;
}
}
}

留邮箱发源码 我最近也在做这个项目 要的话mail我540822453@qq.com

接收客户端这个地方没有头绪.

为什么要这么做?