请问如何为 javamail 设置 socks 代理？

在 JavaMail 中设置 SOCKS 代理需要一些额外的配置，因为 JavaMail 本身并不直接支持 SOCKS 代理。但是，你可以通过配置 Java 的 java.net.Socket 工厂来使用 SOCKS 代理。

以下是如何为 JavaMail 设置 SOCKS 代理的步骤：

import javax.mail.*;
import javax.mail.internet.*;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Proxy;
import java.net.Socket;

public class JavaMailWithSocksProxy {

    // 自定义 Transport，以便使用带SOCKS代理的Socket
    public static class SocksTransport extends Transport {

        private Transport delegate;
        private final Proxy proxy;

        public SocksTransport(Session session, URLName urlname, Proxy proxy) {
            super(session, urlname);
            this.proxy = proxy;
            try {
                delegate = session.getTransport(urlname);
            } catch (NoSuchProviderException e) {
                throw new RuntimeException("Failed to get Transport", e);
            }
        }

        @Override
        public void connect(String host, int port, String user, String password) throws MessagingException {
            try {
                Socket socket = new Socket(proxy);
                socket.connect(new InetSocketAddress(host, port));
                delegate.connect(host, port, user, password);
            } catch (IOException e) {
                throw new MessagingException("Failed to connect via SOCKS proxy", e);
            }
        }

        // 重写其他必要的方法以委托给delegate，或根据需求实现...
    }

    public static void main(String[] args) {
        // 设置SOCKS代理信息
        String proxyHost = "socks-proxy.example.com";
        int proxyPort = 1080;
        Proxy proxy = new Proxy(Proxy.Type.SOCKS, new InetSocketAddress(proxyHost, proxyPort));

        // 创建JavaMail会话
        Properties props = new Properties();
        props.put("mail.smtp.host", "smtp.example.com");
        props.put("mail.smtp.port", "25");
        props.put("mail.smtp.auth", "true");

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

        try {
            // 动态注册自定义的Transport
            session.setProtocolForAddress("smtp", SocksTransport.class.getName());

            // 使用自定义的Transport发送邮件
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("sender@example.com"));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("recipient@example.com"));
            message.setSubject("Test mail with SOCKS proxy");
            message.setText("This is a test mail sent using JavaMail with SOCKS proxy.");

            Transport.send(message);
            System.out.println("Mail sent successfully.");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}