Unable to send Mails using Java Mail API [Using Gmail]

Question

I have used following code which was working fine in year 2014 but currently its not working.

Credentials used in this code are also correct.

public class SendMail 
{  
public void SendMailToTheUserWhoHaveForgotThePassword(String MailTo,String Password)
  {      
      String to = MailTo;  
      String from = "chatna06062016@gmail.com";
      final String username = "chatna06062016";     
      final String password = "xxxxxxxx";  

      String host = "smtp.gmail.com";  
      Properties props = new Properties();
      props.put("mail.smtp.auth", "true");
      props.put("mail.smtp.starttls.enable", "true"); 
      props.put("mail.smtp.host", host);   
      props.put("mail.smtp.port", "25");  
      Session session = Session.getInstance(props,new javax.mail.Authenticator() 
                    {             
                        protected PasswordAuthentication getPasswordAuthentication() 
                        {                
                            return new PasswordAuthentication(username, password);     
                        }          
                    }
                                            );  

      try 
      {   
          Message message = new MimeMessage(session);            
          message.setFrom(new InternetAddress(from));       
          message.setRecipients(Message.RecipientType.TO,InternetAddress.parse(to));        
          message.setSubject("FORGOTTEN PASSWORD"); 


          message.setText("Dear User The Password that you have forgotten is <b>"+Password +"</b>"+ 
                "This email is sended you by using JavaMailAPI "
                  + "HAVE A NICE DAY"
                  + "DO USE THIS SERVICE WHENEVER YOU NEED IT");  

    Transport.send(message);  
      System.out.println("Sent message successfully...."); 

      }
      catch (MessagingException e) { 
         throw new RuntimeException(e); 
      }

       }

} 

I have got email from google like this on the usage of the method used in above class.

Hi ChatNa,
Someone just tried to sign in to your Google Account chatna06062016@gmail.com from an app that doesn't meet modern security standards.
    Details:
Sunday, June 26, 2016 12:57 PM (India Standard Time)
Noida, Uttar Pradesh, India*
We strongly recommend that you use a secure app, like Gmail, to access your account. All apps made by Google meet these security standards. Using a less secure app, on the other hand, could leave your account vulnerable. Learn more.

Google stopped this sign-in attempt, but you should review your recently used devices:

What to do now unable to find out anything helpful anywhere.

Answer 1

The main issue here is that you are logging directly into the SMTP/IMAP mail server using the users login and password. This is not secure.

You should consider switching to useing XOauth2 then you can verify your application and it will no longer be considered insecure.

The XOAUTH2 mechanism allows clients to send OAuth 2.0 access tokens to the server. The protocol uses encoded values shown in the following sections.

    [connection begins]
    C: C01 CAPABILITY
    S: * CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA XLIST
    CHILDREN XYZZY SASL-IR AUTH=XOAUTH2 AUTH=XOAUTH
    S: C01 OK Completed
    C: A01 AUTHENTICATE XOAUTH2 dXNlcj1zb21ldXNlckBleGFtcGxlLmNvb
    QFhdXRoPUJlYXJlciB5YTI5LnZGOWRmdDRxbVRjMk52YjNSbGNrQmhkSFJoZG
    1semRHRXVZMjl0Q2cBAQ==
    S: A01 OK Success
    [connection continues...]

Option number to was mentioned by others Just enable less secure apps. You can read all about it here Less secure apps & your Google Account and the dangers associated with enabling it.

Answer 2

you may need to do following setting in the gmail account:

goto : myaccount -> signIn & security -> connected apps & sites -> Allow less secure apps: ON