我正在尝试使用公司的邮件服务器发送电子邮件。但是我收到以下异常

Caused by: com.sun.mail.smtp.SMTPSendFailedException: 530 5.7.1 Client was not authenticated
    at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:1388)
    at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:959)
    at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:583)
    at javax.mail.Transport.send0(Transport.java:169)
    at javax.mail.Transport.send(Transport.java:98)

这是我的示例代码，

Properties props = System.getProperties();

// Setup mail server
props.put("mail.smtp.host", "example.server.com");
props.put("mail.smtp.auth", "true");
props.put("mail.debug", "true");
props.put("mail.smtp.port", "25");
// Get session
//Session session = Session.getDefaultInstance(props, null);
Session session = Session.getDefaultInstance(props,
    new javax.mail.Authenticator() {
        protected PasswordAuthentication getPasswordAuthentication() {
            return new PasswordAuthentication("username", "password");
        }
    });

// Define message
MimeMessage message = new MimeMessage(session);

// Set the from address
message.setFrom(new InternetAddress(from));

// Set the to address
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));

// Set the subject
message.setSubject("Hello JavaMail");

// Set the content
message.setText("Welcome to JavaMail");

// Send message
Transport.send(message);

哪段代码是错误的？作为用户名和密码，我正在使用公司的电子邮件地址和密码。