1. 确认邮箱账号和密码是否正确。

2. 确认邮箱服务商是否开启了IMAP/POP3服务。

3. 检查代码中是否正确配置了SMTP/IMAP/POP3的相关参数。

参考代码：

使用JavaMail发送邮件：

String host = "smtp.gmail.com";
String port = "587";
String username = "your-email-address@gmail.com";
String password = "your-email-password";

Properties properties = new Properties();
properties.put("mail.smtp.starttls.enable", "true");
properties.put("mail.smtp.host", host);
properties.put("mail.smtp.port", port);
properties.put("mail.smtp.auth", "true");

Session session = Session.getInstance(properties,
        new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

try {
    Message message = new MimeMessage(session);
    message.setFrom(new InternetAddress("your-email-address@gmail.com"));
    message.setRecipients(
            Message.RecipientType.TO,
            InternetAddress.parse("recipient-email-address@example.com")
    );
    message.setSubject("Testing JavaMail API");
    message.setText("Dear Recipient," +
            "\n\nThis is a test email sent using JavaMail API. " +
            "Please do not reply to this email." +
            "\n\nThank you." +
            "\n\nBest regards," +
            "\nYour Name");

    Transport.send(message);

    System.out.println("Email sent successfully.");

} catch (MessagingException e) {
    e.printStackTrace();
}

使用JavaMail接收邮件：

String host = "imap.gmail.com";
String port = "993";
String username = "your-email-address@gmail.com";
String password = "your-email-password";

Properties properties = new Properties();
properties.put("mail.imap.host", host);
properties.put("mail.imap.port", port);
properties.put("mail.imap.starttls.enable", "true");
properties.put("mail.imap.socketFactory.class", "javax.net.ssl.SSLSocketFactory");

Session session = Session.getInstance(properties,
        new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

try {
    Store store =