报错：Could not connect to SMTP host: smtp.qq.com, port: 587
配置文件：
#邮件服务器
spring.mail.host=smtp.qq.com
spring.mail.port=587
spring.mail.username=
spring.mail.password=
spring.mail.protocol=smtp
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.ssl.enable=true
spring.mail.properties.mail.smtp.starttls.enable=true
spring.mail.properties.mail.smtp.socketFactory.port=587
spring.mail.properties.mail.smtp.socketFactory.class=javax.net.ssl.SSLSocketFactory
