com.sun.mail.util.MailConnectException: Couldn't connect to host异常解决

最近在做一个接口项目，需要捕获所有的异常信息，并发送邮件给管理员。使用了JavaMail来实现，然后发现在本地（windows环境）上可以正常发送邮件，而放到了linux环境上就无法发送邮件。相关错误如下：

org.springframework.mail.MailSendException: Mail server connection failed; nested exception is com.sun.mail.util.MailConnectException: Couldn't connect to host, port: 220.181.15.111, 25; timeout -1;nested exception is:java.net.ConnectException: Connection timed out (Connection timed out). Failed messages: com.sun.mail.util.MailConnectException: Couldn't connect to host, port: 220.181.15.111, 25; timeout -1; nested exception is: java.net.ConnectException: Connection timed out (Connection timed out) at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:446) ~[spring-context-support-5.0.6.RELEASE.jar:5.0.6.RELEASE]

重要信息Failed messages: com.sun.mail.util.MailConnectException: Couldn't connect to host和25。首先想到的是linux的端口25没有开通，遂联系相关人员开通，但是可能出于安全考虑没有同意开通。 
没办法，只能更换端口了，需要对配置进行修改 
原始配置

1. spring.mail.host=220.181.15.111 #smtp.126.com 的ip地址
2. spring.mail.username=邮箱
3. spring.mail.password=权限密码
4. spring.mail.default-encoding=UTF-8

修改为

1. spring.mail.host=220.181.15.111
2. spring.mail.username=邮箱
3. spring.mail.password=权限密码
4. spring.mail.default-encoding=UTF-8
5. spring.mail.properties.mail.smtp.auth=true
6. spring.mail.properties.mail.smtp.starttls.enable=true
7. spring.mail.properties.mail.smtp.starttls.required=true
8. spring.mail.port=465
9. spring.mail.properties.mail.smtp.socketFactory.port = 465
10. spring.mail.properties.mail.smtp.socketFactory.class = javax.net.ssl.SSLSocketFactory
11. spring.mail.properties.mail.smtp.socketFactory.fallback = false

之后就可以正常发送邮件了。 
而且在linux中可能会出现无法解析域名的问题，这时候可以将smtp主机域名修改为ip地址。ip地址可以使用命令行的ping命令来获取，如下： 

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顺便讲下spring boot 使用JavaMail发送邮件的方式吧。 
首先添加依赖

1. <dependency>
2.     <groupId>org.springframework.boot</groupId>
3.     <artifactId>spring-boot-starter-mail</artifactId>
4. </dependency>

然后在配置文件(application.properties)中添加mail配置

1. spring.mail.host=220.181.15.111
2. spring.mail.username=邮箱
3. spring.mail.password=权限密码
4. spring.mail.default-encoding=UTF-8
5. spring.mail.properties.mail.smtp.auth=true
6. spring.mail.properties.mail.smtp.starttls.enable=true
7. spring.mail.properties.mail.smtp.starttls.required=true
8. spring.mail.port=465
9. spring.mail.properties.mail.smtp.socketFactory.port = 465
10. spring.mail.properties.mail.smtp.socketFactory.class = javax.net.ssl.SSLSocketFactory
11. spring.mail.properties.mail.smtp.socketFactory.fallback = false

1. @Autowired  
2. JavaMailSender mailSender; //添加依赖后可以直接引用
3. public void sendMail(String emailForm,String[] emailTo,String title,String context){
4.     MimeMessage mimeMessage = mailSender.createMimeMessage();
5.     MimeMessageHelper helper;
6.     try {
7.         helper = new MimeMessageHelper(mimeMessage, true);
8.         helper.setFrom(emailForm);
9.         helper.setTo(emailTo);
10.         helper.setSubject(title);//主题
11.         helper.setText(context);//正文
12.         mailSender.send(mimeMessage);
13.     } catch (MessagingException e1) {
14.         // TODO Auto-generated catch block
15.         e1.printStackTrace();
16.     }
17. }