Simple SMTP Client and POP3 Client in Java

Introduction

In this tip, I will show you how to program a simple SMTP client and POP3 client using Java. These programs are used to send and receive to/from an Email Server.

Background

(Optional) These programs are coded according to the Simple Mail Transfer Protocol and Post Office Protocol.

Using the Code

SMTP Client: The function to send Email:

//
 public void send(int numOfMails) throws Exception    {
            
        String message = "";
        System.out.println("Connecting to server ...");
        
        os.writeBytes("HELO\r\n");            
        int status = 0;//HELO already sent to the server
        int count = 0;           
        
        while(true){
            
            message = bufReader.readLine();    
            System.out.println(message);
            
            if(count>=numOfMails)break;
            
            if(message.contains("Aba he")){
                System.out.println("Close the connection");
                break;
            }
            
            System.out.println("Email count: " + count);
                        
            switch (status) {
                        
            case HELO_RECEIVED: //command HELO already accepted by server
                message = bufReader.readLine();                    
                os.writeBytes("MAIL FROM:"+ this.sender + "\r\n");
                status = 1;
                break;                                    
                
            case MAILFROM_RECEIVED : //command MAIL FROM already accepted by server
                os.writeBytes("RCPT TO:"+ this.receiver + "\r\n");
                status = 2;
                break;
                
            case RCPTTO_RECEIVED : //command RCPT TO already accepted by server
                os.writeBytes("DATA\r\n");        
                status = 3;
                break;
                
            case DATA_RECEIVED : //send email body                    
                os.writeBytes(this.body+"\r\n" + "." + "\r\n");
                count++;
                status=1;                
                break;                                
            }                        
        }
            
        os.writeBytes("QUIT\r\n");
        message = bufReader.readLine();    
        System.out.println(message);
        
        System.out.println("Client terminates the connection!");        
    }

Points of Interest

To test the applications, you may download ArgoSoft Mail Server and setup an account. You then connect the Java programs to the Email server by customizing your parameters.

You can use the code to send multiple emails to an email server. This sounds like a flood attack, but you are advised not to do so.

History

• 10^th May, 2016: Initial version