final String SSL_FACTORY = "javax.net.ssl.SSLSocketFactory";
// 이메일 객체생성하기
Properties props = System.getProperties();
props.setProperty("mail.smtp.host", "smtp.gmail.com");
props.setProperty("mail.smtp.socketFactory.class", SSL_FACTORY);
props.setProperty("mail.smtp.socketFactory.fallback", "false");
props.setProperty("mail.smtp.port", "465");
props.setProperty("mail.smtp.socketFactory.port", "465");
props.put("mail.smtp.auth", "true");
props.put("mail.debug", "true");
props.put("mail.store.protocol", "pop3");
props.put("mail.transport.protocol", "smtp");
final String username = "인증받은 이메일";//
final String password = "2단계인증에서 받은 비번";

try{
    Session session = Session.getDefaultInstance(props,
    new Authenticator(){
    protected PasswordAuthentication getPasswordAuthentication() {
    return new PasswordAuthentication(username, password);
}});

//메세지 설정
Message msg = new MimeMessage(session);

//보내는사람 받는사람 설정
msg.setFrom(new InternetAddress("보내는사람@이메일"));
msg.setRecipients(Message.RecipientType.TO,
					InternetAddress.parse("받는사람@이메일",false));
msg.setSubject("제목입니다");
msg.setText("\n내용입니다");
msg.setSentDate(new Date());
Transport.send(msg);
System.out.println("발신성공!");

}catch (MessagingException error){
	System.out.println("에러가 발생했습니다: " + error);
}