Java 发送邮件，基于Apache mail

		# jar包，maven
		<dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-email</artifactId>
            <version>1.5</version>
        </dependency>

package com.example.demo;

import org.apache.commons.mail.EmailException;
import org.apache.commons.mail.HtmlEmail;
import org.apache.commons.mail.SimpleEmail;

import java.io.File;
import java.security.SecureRandom;
import java.util.Date;
import java.util.Random;

public class EmailUtil {

    private final static String USERNAME = "******@qq.com";//自己注册的发件人邮箱
    private final static String PASSWORD = "*********"; // POP3/SMTP服务授权码
    private final static String ADDRESS = "smtp.qq.com";       //qq邮箱固定名称
    private final static Integer PORT = 587; //邮箱端口为465/587
//    private final static String USERNAME = "**********@163.com";
//    private final static String ADDRESS = "smtp.163.com";
//    private final static String PASSWORD = "***********";
//    private final static Integer PORT = 25;

    /**
     * 随机对象
     */
    private static final Random RANDOM = new SecureRandom();
    private static final String NUMBER = "0123456789";
    private final static String CHARSET = "UTF8";
    
    /**
     * 发送邮件给指定人，需要HTML内容
     * @param user
     * @param title
     */
    public static void sendHtmlMail(String user, String title){
        HtmlEmail htmlEmail = new HtmlEmail();
        htmlEmail.setCharset(CHARSET);
        htmlEmail.setHostName(ADDRESS);
        htmlEmail.setSmtpPort(PORT);
        htmlEmail.setAuthentication(USERNAME, PASSWORD);
        try {
            htmlEmail.setFrom(USERNAME);
            htmlEmail.addTo(user);
            htmlEmail.setSubject(title);
            String cid = htmlEmail.embed(new File("图片全路径"));
            htmlEmail.setHtmlMsg("<div style='color:red;font-size:200px'>HTML内容</div> <img src='cid:" + cid + "' />");
            htmlEmail.send();
        } catch (EmailException e) {
            e.printStackTrace();
        }
    }
    /**
     * 发送邮件给指定人，需要主题和内容
     * @param user
     * @param title
     * @param content
     */
    public static void sendSimpleMail(String user, String title, String content) {
        SimpleEmail email = new SimpleEmail();
        email.setCharset(CHARSET);
        email.setHostName(ADDRESS);
        email.setSmtpPort(PORT);
        email.setAuthentication(USERNAME, PASSWORD);
        try {
            email.setFrom(USERNAME);
            email.addTo(user);
            email.setSubject(title);
            email.setMsg(content);
            email.send();
        } catch (EmailException e) {
            e.printStackTrace();
        }
    }

    /**
     * 六位数验证码
     */
    public static String randSendCode(){
        char[] nonceChars = new char[6];
        for (int index = 0; index < nonceChars.length; ++index) {
            nonceChars[index] = NUMBER.charAt(RANDOM.nextInt(10));
        }
        return new String(nonceChars);
    }

    /**
     * 发送验证邮件给用户
     * @param user
     * @param code
     */
    public static void sendValidateMail(String user, String code) {
        String title = "注册验证码";
        String content = "感谢您注册，您的验证码为 \n" + code + "\n请注意保存，此验证码有效期为 10分钟 。";
        sendSimpleMail(user, title, content);
    }


    public static void main(String[] args) {
        // 接收人有限，不限邮箱平台，QQ，网易，谷歌邮箱都可以
        //String to = "******@qq.com";
        //收件人和消息
        //sendValidateMail(to, randSendCode());
        //sendHtmlMail(to,"活动促销");
    }
}

关于授权码如何获取，请各位百度搜索了
以下是SMTP各个邮件服务平台的端口号和服务HOST
请参考：https://blog.youkuaiyun.com/hssdw25172008/article/details/8729469
各个邮件服务SMTP地址和端口号