send mail to Gmail account

问题:

I am sending mail from my Java app to Gmail Account. I had used the Java Mail API and it worked fine. But is it possible to send an e-mail without using the mail API in java?

I mean just by using sockets:

public class Main {
  public static void main(String[] args) throws Exception {
    String host = "smtp.gmail.com";
    int port = 465;
    String from = "[e-mail]";
    String toAddr = "[e-mail]";


    Socket servSocket = new Socket(host, port);
    DataOutputStream os = new DataOutputStream(servSocket.getOutputStream());
    DataInputStream is = new DataInputStream(servSocket.getInputStream());

    if (servSocket != null && os != null && is != null) {
      os.writeBytes("HELO\r\n");
      os.writeBytes("MAIL From:" + from + " \r\n");
      os.writeBytes("RCPT To:" + toAddr + "\r\n");
      os.writeBytes("DATA\r\n");
      os.writeBytes("X-Mailer: Java\r\n");
      os.writeBytes("DATE: " + DateFormat.getDateInstance(DateFormat.FULL, 
                                   Locale.US).format(new Date()) + "\r\n");
      os.writeBytes("From:" + from + "\r\n");
      os.writeBytes("To:" + toAddr + "\r\n");
    }

    os.writeBytes("Subject:\r\n");
    os.writeBytes("body\r\n");
    os.writeBytes("\r\n.\r\n");
    os.writeBytes("QUIT\r\n");
    String responseline;
    while ((responseline = is.readUTF()) != null) { 
      if (responseline.indexOf("Ok") != -1)
        break;
    }
  }
}

But it is not working, it doesn't send out the mail. Can anyone tell me what could be the problem?

回答1:

Here is a good example:

public class SMTPDemo {

  public static void main(String args[]) throws IOException,
      UnknownHostException {
    String msgFile = "file.txt";
    String from = "[e-mail]";
    String to = "[e-mail]";
    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;
    }
  }
}

-> http://www.java2s.com/Code/Java/Network-Protocol/SendingMailUsingSockets.htm

回答2:

If you have a dynamic IP you are probably not able to send messages to Googlemail.

回答3:

GMail doesn't allow non-secure mail transfer. You need to make an SSL/TLS connection in your implementation.

回答4:

By default, Google only allows encrypted connections. That's actually a good thing, in my opinion.

But if you must send your mails in plaintext, you can enable it on your Account Page under settings.

回答5:

In order to use a secure connection, use SSLSocket instead of Socket, like this:

SSLSocket socket = (SSLSocket) ((SSLSocketFactory) SSLSocketFactory.getDefault()).createSocket(InetAddress.getByName("smtp.gmail.com"), 465);