<dependencies>
????<dependency>
????????<groupId>org.springframework.boot</groupId>
????????<artifactId>spring-boot-starter-mail</artifactId>
????</dependency>
????<dependency>
????????<groupId>org.springframework.boot</groupId>
????????<artifactId>spring-boot-starter-test</artifactId>
????????<scope>test</scope>
????</dependency>
</dependencies>

pom.xml里的
<!--?https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-mail?-->
<dependency>
???<groupId>org.springframework.boot</groupId>
???<artifactId>spring-boot-starter-mail</artifactId>
???<version>2.1.3.RELEASE</version>
</dependency>

import導入的
import?org.springframework.mail.SimpleMailMessage;

可以看一下有沒有導入錯的