Java手动实现SMTP邮件发送：EHLO与AUTH PLAIN认证详解

echo -ne '\0000your_username\0000your_password' | openssl base64

echo -ne '\0000test@naver.com\0000mysecretpassword' | openssl base64

import java.util.Base64;

// ...
String username = "your_username@example.com";
String password = "your_password";
String authString = "\000" + username + "\000" + password;
String encodedAuthString = Base64.getEncoder().encodeToString(authString.getBytes());
// ...

import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.SSLSocket;
import java.io.*;
import java.net.*;
import java.util.Base64; // 引入Base64类

class MailServer {

    // 请替换为你的实际邮箱用户名和密码
    private static final String USERNAME = "your_username@naver.com";
    private static final String PASSWORD = "your_password";

    public static void MailSender() throws Exception {
        String Reply;
        String To = "recipient@example.com"; // 收件人邮箱
        String From = USERNAME; // 发件人邮箱，通常与认证用户名一致
        String Data = "Subject: Hello from Java SMTP Client\r\n\r\nHello this is computer networking."; // 邮件内容，包含Subject和空行

        SSLSocketFactory sslsocketf = (SSLSocketFactory) SSLSocketFactory.getDefault();
        System.out.println("Connect Start");
        // 连接到SMTP服务器的SSL端口，通常是465
        SSLSocket socket = (SSLSocket) sslsocketf.createSocket("smtp.naver.com", 465);
        System.out.println("Connect Success");

        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintWriter outToServer = new PrintWriter(socket.getOutputStream(), true);

        // 接收服务器的初始欢迎信息
        Reply = inFromServer.readLine();
        if (Reply.startsWith("220")) {
            System.out.println("Server Connect Success!");
        } else {
            System.out.println("Server Connect Fail");
            System.exit(0);
        }
        System.out.println(Reply);

        // EHLO命令 - 替换HELO，获取服务器扩展功能
        outToServer.println("EHLO naver.com"); // 使用你的域名或IP地址
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "250"); // 检查EHLO响应

        // AUTH PLAIN命令 - 进行身份认证
        String authString = "\000" + USERNAME + "\000" + PASSWORD;
        String encodedAuthString = Base64.getEncoder().encodeToString(authString.getBytes("UTF-8")); // 指定UTF-8编码
        outToServer.println("AUTH PLAIN " + encodedAuthString);
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "235"); // 235表示认证成功

        // MAIL FROM command
        outToServer.println("MAIL FROM: <" + From + ">");
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "250");

        // RCPT TO command
        outToServer.println("RCPT TO: <" + To + ">");
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "250");

        // DATA command
        outToServer.println("DATA");
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "354"); // 354表示可以开始发送邮件内容
        outToServer.println(Data);
        outToServer.println("."); // 邮件内容结束标志
        Reply = inFromServer.readLine(); // 读取DATA命令后的响应
        ReplyCheck(Reply, "250"); // 250表示邮件接受成功

        // QUIT command
        outToServer.println("QUIT");
        Reply = inFromServer.readLine();
        ReplyCheck(Reply, "221"); // 221表示服务器关闭连接

        outToServer.close();
        inFromServer.close();
        socket.close();
    }

    public static void ReplyCheck(String Reply, String Status) throws Exception {
        System.out.println(Reply);
        if (!Reply.startsWith(Status)) {
            throw new Exception(Reply);
        }
    }

    public static void main(String args[]) {
        try {
            MailServer.MailSender();
            System.out.println("Send Mail Success!");
        } catch (Exception e) {
            System.out.println("Send Mail Fail");
            System.out.println(e.toString());
        }
    }
}