<dependency>

   <groupId>org.springframework.boot</groupId>

   <artifactId>spring-boot-starter-mail</artifactId>

  </dependency>

spring.mail.host = smtp.gmail.com

spring.mail.username = xxxx@gmail.com

spring.mail.password = xxxx

send.from.email= xxxx@gmail.com

spring.mail.properties.mail.smtp.auth = true;

spring.mail.properties.mail.smtp.starttls.enable = true

spring.mail.properties.mail.smtp.ssl.enable = true

spring.mail.properties.mail.socketFactory.port=587

spring.mail.properties.mail.socketFactory.class=javax.net.ssl.SSLSocketFactory

spring.mail.properties.mail.socketFactory.fallback=false

spring.mail.smtp.port= 587

package com.example.demo.controller;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.ResponseBody;

import com.example.demo.service.MailService;

@Controller

public class MailController {

  @Autowired

 private MailService mailService;

 @GetMapping("/")

 @ResponseBody

 public String hello(){

  mailService.prepareAndSend("053792@fju.edu.tw","Sample mail subject");

  return "Mail sent";

 }

}

package com.example.demo.service;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.mail.MailException;

import org.springframework.mail.javamail.JavaMailSender;

import org.springframework.mail.javamail.MimeMessageHelper;

import org.springframework.mail.javamail.MimeMessagePreparator;

import org.springframework.stereotype.Service;

@Service

public class MailService {

    private JavaMailSender mailSender;

    @Autowired

    public MailService(JavaMailSender mailSender) {

        this.mailSender = mailSender;

    }

    public void prepareAndSend(String recipient, String message) {

       MimeMessagePreparator messagePreparator = mimeMessage -> {

             MimeMessageHelper messageHelper = new MimeMessageHelper(mimeMessage);

             messageHelper.setFrom("jitsung.wu@gmail.com");

             messageHelper.setTo(recipient);

             messageHelper.setSubject(message);

             messageHelper.setText(message);

         };

         try {

             mailSender.send(messagePreparator);

             //System.out.println("sent");

         } catch (MailException e) {

             //System.out.println(e);

             // runtime exception; compiler will not force you to handle it

         }

    }

}