Email Server Monitoring Methods

Question

I am about to develop an Email Server monitoring project. I have several questions about it:
1. Whats the best method to do it ? (in term of accuracy and work load)
2. I've been reading on some round-robin method which expect a reply from an email server to determine the status of the server. Whats the difference between this method and the conventional way (which sends email to server and doesnt expect for a reply), Isn't the latter method sufficient and accurate enough ?
Thats what I'd like to know. Any other suggestions are also welcome. Thanks.

Answer 1

import java.io.*;
import java.net.Socket;
* Simple SMTP Client that allows your Java App send emails.
* Uses Java Sockets to connect directly to an SMTP server.
* It supports sending of plain text or HTML emails.
* Bonus: Unlike many other Java SMTP Sockets examples, this one actually works.
* @author Olly Oechsle, www.intelligent-web.co.uk
public class Emailer {
    public static void main(String[] args) throws Exception {
        String results = send("localhost",
                25,
                "[email protected]",
                "[email protected]",
                "Test Email",
                "<b>You got mail!</b>");
        System.out.println(results);
     * Sends an email.
     * @return The full SMTP conversation as a string.
    public static String send(
            String host,
            int port,
            String to,
            String from,
            String subject,
            String message) throws Exception {
        // Save the SMTP conversation into this buffer (for debugging if necessary)
        StringBuffer buffer = new StringBuffer();
        try {
            // Connect to the SMTP server running on the local machine. Usually this is SendMail
            Socket smtpSocket = new Socket(host, port);
            // We send commands TO the server with this
            DataOutputStream output = new DataOutputStream(smtpSocket.getOutputStream());
            // And recieve responses FROM the server with this
            BufferedReader input =
                    new BufferedReader(
                            new InputStreamReader(
                                    new DataInputStream(smtpSocket.getInputStream())));
            try {
                // Read the server's hello message
                read(input, buffer);
                // Say hello to the server
                send(output, "HELO localhost.localdomain\r\n", buffer);
                read(input, buffer);
                // Who is sending the email
                send(output, "MAIL FROM: " + from + "\r\n", buffer);
                read(input, buffer);
                // Where the mail is going
                send(output, "RCPT to: " + to + "\r\n", buffer);
                read(input, buffer);
                // Start the message
                send(output, "DATA\r\n", buffer);
                read(input, buffer);
                // Set the subject
                send(output, "Subject: " + subject + "\r\n", buffer);
                // If we detect HTML in the message, set the content type so it displays
                // properly in the recipient's email client.
                if (message.indexOf("<") == -1) {
                    send(output, "Content-type: text/plain; charset=\"us-ascii\"\r\n", buffer);
                } else {
                    send(output, "Content-type: text/html; charset=\"us-ascii\"\r\n", buffer);
                // Send the message
                send(output, message, buffer);
                // Finish the message
                send(output, "\r\n.\r\n", buffer);
                read(input, buffer);
                // Close the socket
                smtpSocket.close();
            catch (IOException e) {
                System.out.println("Cannot send email as an error occurred.");
        catch (Exception e) {
            System.out.println("Host unknown");
        return buffer.toString();
     * Sends a message to the server using the DataOutputStream's writeBytes() method.
     * Saves what was sent to the buffer so we can record the conversation.
    private static void send(DataOutputStream output,
                             String data,
                             StringBuffer buffer)
            throws IOException {
        output.writeBytes(data);
        buffer.append(data);
     * Reads a line from the server and adds it onto the conversation buffer.
    private static void read(BufferedReader br, StringBuffer buffer) throws IOException {
        int c;
        while ((c = br.read()) != -1) {
            buffer.append((char) c);
            if (c == '\n') {
                break;
}Is the above code considered as low level approach ?
I tested it so far and it works only for some mail servers (https://inetmon.com and https://nav6.org). However when I tried to send an email to myself in gmail.com it doesnt work. It catches an expection and prints "Host Unknown". Any idea how to fix it ?