@ConfigurationProperties失效的几种情况看看你是那种

1：yml文件换成properties文件

2：pom.xml添加

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-configuration-processor</artifactId>
    <optional>true</optional>
</dependency>

3：添加插件

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
</plugin>

4：启动类添加@EnableConfigurationProperties({MailProperties.class})