Could not connect to SMTP host:

第一种、云服务器封禁了25端口，代码改用465

final String smtpPort = "465";
prop.setProperty("mail.smtp.port", smtpPort);
prop.setProperty("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory");
prop.setProperty("mail.smtp.socketFactory.fallback", "false");
prop.setProperty("mail.smtp.socketFactory.port", smtpPort);

也就是加入了SSL验证。

第二种、修改Spring配置

spring:
      mail:
          host: 
          username: 
          password: 
          default-encoding: utf-8

例子：
xxx@qq.com

spring:
mail:
host: smtp.qq.com #发送邮件服务器
username: xx@qq.com #QQ邮箱
password: xxxxxxxxxxx #客户端授权码
protocol: smtp #发送邮件协议
properties.mail.smtp.auth: true
properties.mail.smtp.port: 465 #端口号465或587
properties.mail.display.sendmail: Javen #可以任意
properties.mail.display.sendname: Spring Boot Guide Email #可以任意
properties.mail.smtp.starttls.enable: true
properties.mail.smtp.starttls.required: true
properties.mail.smtp.ssl.enable: true
default-encoding: utf-8
from: xx@qq.com #与上面的username保持一致,这个是发送邮件方

xxx@126.com

spring:
mail:
host: smtp.126.com
username: xx@126.com
password: xxxxxxxx
protocol: smtp
properties.mail.smtp.auth: true
properties.mail.smtp.port: 994 #465或者994
properties.mail.display.sendmail: Javen
properties.mail.display.sendname: Spring Boot Guide Email
properties.mail.smtp.starttls.enable: true
properties.mail.smtp.starttls.required: true
properties.mail.smtp.ssl.enable: true
default-encoding: utf-8
from: xx@126.com