Solutions for Mail User Agent: Simplified Version

Solutions for Mail User Agent: Simplified Version

import java.io.*;
import java.net.*;
 
public class EmailSender
{
   public static void main(String[] args) throws Exception
   {
      // Establish a TCP connection with the mail server.
      Socket socket = new Socket("mx1.csusb.edu", 25);
 
      // Create a BufferedReader to read a line at a time.
      InputStream is = socket.getInputStream();
      InputStreamReader isr = new InputStreamReader(is);
      BufferedReader br = new BufferedReader(isr);
 
      // Read greeting from the server.
      String response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("220")) {
         throw new Exception("220 reply not received from server.");
      }
 
      // Get a reference to the socket's output stream.
      OutputStream os = socket.getOutputStream();
 
      // Send HELO command and get server response.
      String command = "HELO x\r\n";
      System.out.print(command);
      os.write(command.getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("250")) {
         throw new Exception("250 reply not received from server.");
      }
 
      // Send MAIL FROM command.
      command = "MAIL FROM: x@aiit.or.kr\r\n";
      System.out.print(command);
      os.write(command.getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("250")) {
         throw new Exception("250 reply not received from server.");
      }
 
      // Send RCPT TO command.
      command = "RCPT TO: dturner@csusb.edu\r\n";
      System.out.print(command);
      os.write(command.getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("250")) {
         throw new Exception("250 reply not received from server.");
      }
 
      // Send DATA command.
      command = "DATA\r\n";
      System.out.print(command);
      os.write(command.getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("354")) {
         throw new Exception("354 reply not received from server.");
      }
 
      // Send message data.
      os.write("SUBJECT: test msg\r\n\r\n".getBytes("US-ASCII"));
      os.write("David,\r\n".getBytes("US-ASCII"));
      os.write("\r\n".getBytes("US-ASCII"));
      os.write("This lab is too hard.\r\n".getBytes("US-ASCII"));
 
      // End with line with a single period.
      os.write(".\r\n".getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
      if (!response.startsWith("250")) {
         throw new Exception("250 reply not received from server.");
      }
 
      // Send QUIT command.
      command = "QUIT\r\n";
      System.out.print(command);
      os.write(command.getBytes("US-ASCII"));
      response = br.readLine();
      System.out.println(response);
   }
}