使用的技术：

• Spring Boot 2.3.2
• Java Mail 1.6.2
• Maven 3
• Java 8

1、添加依赖

spring-boot-starter-mail

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

2、配置 application.properties

这里得注意下了，除了邮件服务商说明同时支持tls或者ssl，否则需要将tls/ssl分开配置,这里我使用得是outlook，所以只支持 tls 587端口，一开始我配置成ssl，走了一个坑。

spring.mail.host=smtp.gmail.com
spring.mail.port=587
spring.mail.username=username
spring.mail.password=password
# Other properties
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.connectiontimeout=5000
spring.mail.properties.mail.smtp.timeout=5000
spring.mail.properties.mail.smtp.writetimeout=5000
# 这里是tls的配置项，如果没有使用587，则要注释掉
# TLS , port 587
spring.mail.properties.mail.smtp.starttls.enable=true
# 这里是ssl的配置项，如果没有使用465，则要注释掉
# SSL, post 465
#spring.mail.properties.mail.smtp.socketFactory.port = 465
#spring.mail.properties.mail.smtp.socketFactory.class = javax.net.ssl.SSLSocketFactory

如果是这个错误，那么就是你把tls/ssl的配置弄反了。
nested exception is:
	javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?. Failed messages: javax.mail.MessagingException: Could not connect to SMTP host: smtp.office365.com, port: 587;
  nested exception is:
	javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?; message exceptions (1) are:
Failed message 1: javax.mail.MessagingException: Could not connect to SMTP host: smtp.office365.com, port: 587;
  nested exception is:
	javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?] with root cause

3、发送文本邮件

import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
    @Autowired
    private JavaMailSender javaMailSender;
    void sendEmail() {
        SimpleMailMessage msg = new SimpleMailMessage();
        msg.setTo("[email protected]", "[email protected]", "[email protected]");
        msg.setSubject("Testing from Spring Boot");
        msg.setText("Hello World \n Spring Boot Email");
        javaMailSender.send(msg);
    }

4、发送html格式的邮件

@GetMapping("sendMail")
void sendMain() throws MessagingException {
    MimeMessage mimeMessage = mailSender.createMimeMessage();
    MimeMessageHelper message = new MimeMessageHelper(mimeMessage, true);
    message.setFrom("浅忆博客(系统)<[email protected]>");
    message.setTo("[email protected]");
    message.setSubject("HTML邮件");
    message.setText("<h1>Check attachment for image!</h1>", true);
    mailSender.send(mimeMessage);
}

5、发送HTML电子邮件和文件附件

import org.springframework.core.io.ClassPathResource;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
    void sendEmailWithAttachment() throws MessagingException, IOException {
        MimeMessage msg = javaMailSender.createMimeMessage();
        // true = multipart message
        MimeMessageHelper helper = new MimeMessageHelper(msg, true);
        helper.setTo("to_@email");
        helper.setSubject("Testing from Spring Boot");
        // default = text/plain
        //helper.setText("Check attachment for image!");
        // true = text/html
        helper.setText("<h1>Check attachment for image!</h1>", true);
        // hard coded a file path
        //FileSystemResource file = new FileSystemResource(new File("path/android.png"));
        helper.addAttachment("my_photo.png", new ClassPathResource("android.png"));
        javaMailSender.send(msg);
    }

参考文章:
https://mkyong.com/spring-boot/spring-boot-how-to-send-email-via-smtp/