java.lang.IllegalStateException: Found multiple @SpringBootConfiguration annotated classes 出现这个异常是怎么回事呀

package com.ep.email.hello;

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.stereotype.Service;

@Service
public class MailService {

    @Value("${spring.mail.username}")
    private String from;

    @Autowired
    private JavaMailSender mailSender;

    public void sayHello(){
        System.out.println("hello springboot!");
    }

    public void sendSimpleMail(String to,String subject,String content){

        SimpleMailMessage message=new SimpleMailMessage();
        message.setTo(to);
        message.setSubject(subject);
        message.setText(content);
        message.setFrom(from);

        mailSender.send(message);
    }

}

spring.mail.host=smtp.126.com
spring.mail.username=ityouknow@126.com
spring.mail.password=yourPassword126
spring.mail.default-encoding=UTF-8

pom.xml也配置了依赖mail