JAVA Mail - 用户名，密码，主机

Question

我有以下代码

private void emailFile(){
        // Recipient's email ID needs to be mentioned.
        String to = "destinationemail@gmail.com";

        // Sender's email ID needs to be mentioned
        String from = "fromemail@gmail.com";

        final String username = "manishaspatil";//change accordingly
        final String password = "******";//change accordingly

        // Assuming you are sending email through relay.jangosmtp.net
        String host = "relay.jangosmtp.net";

        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");

    .....
}

我想知道什么是username，password（它与我的电子邮件密码相同或者是什么？），host以及（host之间的区别}，username和from）。