这是一个很好的例子：
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 donen"); } 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; } }}-> http://www.java2s.com/Code/Java/Network-Protocol/SendingMailUsingSockets.htm
