A question about sending email from java program

Question

I need to send email from java program. I am first trying to understand basics. I found a snippet at:

https://www.javatpoint.com/example-of-sending-email-using-java-mail-api

import java.util.*;  
import javax.mail.*;  
import javax.mail.internet.*;  
import javax.activation.*;  
  
public class SendEmail  
{  
 public static void main(String [] args){  
      String to = "sonoojaiswal1988@gmail.com";//change accordingly  
      String from = "sonoojaiswal1987@gmail.com";change accordingly  
      String host = "localhost";//or IP address  
  
     //Get the session object  
      Properties properties = System.getProperties();  
      properties.setProperty("mail.smtp.host", host);  
      Session session = Session.getDefaultInstance(properties);  
  
     //compose the message  
      try{  
         MimeMessage message = new MimeMessage(session);  
         message.setFrom(new InternetAddress(from));  
         message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));  
         message.setSubject("Ping");  
         message.setText("Hello, this is example of sending email  ");  
  
         // Send message  
         Transport.send(message);  
         System.out.println("message sent successfully....");  
  
      }catch (MessagingException mex) {mex.printStackTrace();}  
   }  
}  

My question is that as per the code, it looks like anyone can use any sender email address string and send infinite emails to any receiver email address. I am missing something in my understanding, which will prevent such scenario to happen. Please help.

I understand that this is not a programming question, but guess, it will not take too much time to answer this basic question and don't know any other equally active forum.

Answer 1

This example works for servers which don't need authentication. And this is usually not applicable to the smtp servers used in production. Such servers are used mostly for testing purposes where they are not exposed over the internet. Hence, although its possible to send infinite number of mails as mentioned by you, no one would be interested in doing the same.

For the servers where authentication is necessary, credentials need to be provided. And this is explained in detail in the blog mentioned by you.