在本地主机上发送邮件有效，但是当部署到网络服务器时，我得到无法连接到主机，端口：smtp.gmail.com，587

Question

I know this question is all over the stack overflow but I couldn-t find any answer that works.

I'm trying to send mail from my webApp to gmail account (like contact form) and as it's stated in the title, sending mail on localhost works, but when deployed to webserver I get

com.sun.mail.util.MailConnectException: Couldn't connect to host, port: smtp.gmail.com, 587; timeout -1; nested exception is: java.net.ConnectException: Connection timed out (Connection timed out)

I have freshly installed Ubuntu on Linode VPS running Tomcat 9.

ufw (firewall) is disabled

On gmail account I've enabled

• Less secure app access (it wasn-t working on localhost before this option was enabled)
• POP3
• IMAP

I've also tried enabling 2 factor auth and genereting app password on gmail. Again it worked on, localhost but not when deployed on tomcat.

My code for sending mail:

   Properties props = new Properties();
   props.put("mail.transport.protocol", "smtp");
   props.put("mail.smtp.auth", "true");
   props.put("mail.smtp.starttls.enable", "true");
   props.put("mail.smtp.starttls.required", "true");
   props.put("mail.smtp.host", "smtp.gmail.com");
   props.put("mail.smtp.port", "587"); //I''ve tried with port 25 also..it didn't work
  
   Session session = Session.getInstance(props, new javax.mail.Authenticator() {
      protected PasswordAuthentication getPasswordAuthentication() {
         return new PasswordAuthentication("myMail@gmail.com", "myPassword"); 
         
      }
   });
   Message msg = new MimeMessage(session);
   msg.setFrom(new InternetAddress(mailRequest.getEmail(), mailRequest.getName())); //get email ne radi radi google maila
    
   msg.setReplyTo(new InternetAddress[]{new InternetAddress(mailRequest.getEmail())});
   msg.setRecipients(Message.RecipientType.TO, InternetAddress.parse("myMail@gmail.com"));
   msg.setSubject(mailRequest.getSubject());
   msg.setContent(mailRequest.getMessage(), "text/html");
   msg.setSentDate(new Date());

   MimeBodyPart messageBodyPart = new MimeBodyPart();
   messageBodyPart.setContent(mailRequest.getMessage(), "text/html");

   Multipart multipart = new MimeMultipart();
   multipart.addBodyPart(messageBodyPart);

   msg.setContent(multipart);
   Transport.send(msg);
   
   if (mailRequest.isSendCopyToUser()) {
       Message msgForUser = new MimeMessage(session);
       msgForUser.setFrom(new InternetAddress("myMail@gmail.com", "Galerija Lemaić")); 
        
       msgForUser.setReplyTo(new InternetAddress[]{new InternetAddress("myMail@gmail.com")});
       msgForUser.setRecipients(Message.RecipientType.TO, InternetAddress.parse(mailRequest.getEmail()));
       msgForUser.setSubject(mailRequest.getSubject());
       msgForUser.setContent(mailRequest.getMessage(), "text/html");
       msgForUser.setSentDate(new Date());

       MimeBodyPart messageuserBodyPart = new MimeBodyPart();
       messageuserBodyPart.setContent(mailRequest.getMessage(), "text/html");

       Multipart multipartUser = new MimeMultipart();
       multipartUser.addBodyPart(messageBodyPart);
       msgForUser.setContent(multipartUser);
       Transport.send(msgForUser);
   }
   
   
}

Also I've tried adding this but it didn't help

props.put("mail.store.protocol", "pop3s");
props.put("mail.pop3.host", "pop.gmail.com");     
props.put("mail.pop3.user", "myMail@gmail.com");
props.put("mail.pop3.socketFactory", 995);
props.put("mail.pop3.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
props.put("mail.pop3.port", 995);

I suppose that I have to enable something on Ubuntu or Tomcat, but I'm not sure what

Answer 1

Ok, I've found a solution.

First - Linode VPS (and digital ocean droplets too from what I've read) have restrictions by default on smpt traffic in order to help combat spam on their platform. So you have to contact them through support and ask them to lift those restrictions for your VPS

Second - after allowing less secure apps (or setting up app apsword through gmail) you have to go to https://accounts.google.com/DisplayUnlockCaptcha and click Continue. Basically allowing connection from your app.

Regarding second point. Here is the solution javax.mail.AuthenticationFailedException: 534-5.7.14 <https://accounts.google.com/signin/continue?sarp=1