spring boot邮件找不到自动布线的JavaMailSender

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

spring.mail.host=smtp.example.com
spring.mail.port=587
spring.mail.username=your-email@example.com
spring.mail.password=your-email-password
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

@Configuration
public class MyMailConfig {

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

    @Value("${spring.mail.port}")
    private int port;

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

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

    @Bean
    public JavaMailSender javaMailSender() {
        JavaMailSenderImpl mailSender = new JavaMailSenderImpl();
        mailSender.setHost(host);
        mailSender.setPort(port);
        mailSender.setUsername(username);
        mailSender.setPassword(password);
        return mailSender;
    }
}