API

import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Properties;

/**
 * 发邮件工具类
 */
public final class MailUtils {
    private static final String USER = "max_alice@qq.com"; // 发件人称号，同邮箱地址
    private static final String PASSWORD = "unxxvscmpsaygdaa"; // 如果是qq邮箱可以使户端授权码，或者登录密码
    //private static final String PASSWORD = "1220shihuihui";//IXWEJTAFORVWIUXZ
    //private static final String USER = "max_alice@126.com";
    /**
     *
     * @param to 收件人邮箱
     * @param text 邮件正文
     * @param title 标题
     */
    /* 发送验证信息的邮件 */
    public static boolean sendMail(String to, String text, String title){
        try {
            final Properties props = new Properties();
            props.put("mail.smtp.auth", "true");
            props.put("mail.smtp.host", "smtp.qq.com");

            // 发件人的账号
            props.put("mail.user", USER);
            //发件人的密码
            props.put("mail.password", PASSWORD);

            // 构建授权信息，用于进行SMTP进行身份验证
            Authenticator authenticator = new Authenticator() {
                @Override
                protected PasswordAuthentication getPasswordAuthentication() {
                    // 用户名、密码
                    String userName = props.getProperty("mail.user");
                    String password = props.getProperty("mail.password");
                    return new PasswordAuthentication(userName, password);
                }
            };
            // 使用环境属性和授权信息，创建邮件会话
            Session mailSession = Session.getInstance(props, authenticator);
            // 创建邮件消息
            MimeMessage message = new MimeMessage(mailSession);
            // 设置发件人
            String username = props.getProperty("mail.user");
            InternetAddress form = new InternetAddress(username);
            message.setFrom(form);

            // 设置收件人
            InternetAddress toAddress = new InternetAddress(to);
            message.setRecipient(Message.RecipientType.TO, toAddress);

            // 设置邮件标题
            message.setSubject(title);

            // 设置邮件的内容体
            message.setContent(text, "text/html;charset=UTF-8");
            // 发送邮件
            Transport.send(message);
            return true;
        }catch (Exception e){
            e.printStackTrace();
        }
        return false;
    }

    public static void main(String[] args) throws Exception { // 做测试用
        MailUtils.sendMail("max_alice@126.com","你好，这是一封测试邮件，无需回复。","测试邮件");
        System.out.println("发送成功");
    }



}

spring

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>

package com.example.utils;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;

import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
import java.io.File;

@Component

public class MailUtil {

    @Autowired
    private JavaMailSender javaMailSender;

    @Value("${spring.mail.username}")
    private String from;
    @Async
    public void sendSimpleEmail(String to,String subject,String text){
        SimpleMailMessage message = new SimpleMailMessage();
        //发送人
        message.setFrom(from);
        //接受人
        message.setTo(to);
        //标题
        message.setSubject(subject);

        //正文
        message.setText(text);

        javaMailSender.send(message);

    }
    @Async
    public void sendEmail(String to,String subject,String text) throws MessagingException {
        MimeMessage message = javaMailSender.createMimeMessage();
        MimeMessageHelper helper = new MimeMessageHelper(message,true);
        //发送人

        helper.setFrom(from);
        //接受人
        helper.setTo(to);
        //标题
        helper.setSubject(subject);

        //正文
        helper.setText(text,true);

        //附件
        File f = new File("D:\\studying\\形式与政策\\dog_1.jpg");
        helper.addAttachment("filename.jpg",f);
        javaMailSender.send(message);

    }
}