Java Mail not working in Cloud Server - email

Question

I have a Java EE web application which run on GlassFish server. I have written the following code to send emails through the application.
When I test the application in my home PC and Laptop, it send emails immediately. When I run the very same application in a google cloud server, it gives a time out exception. What can be the possible causes?
package com.divudi.ejb;
import java.util.Properties;
import javax.ejb.Schedule;
import javax.ejb.Stateless;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
#Stateless
public class EmailManagerEjb {
final static String USERNAME = "mygmailaccount#gmail.com";
final static String PASSWORD = "mygmailpassword";
static Session session = null;
public void sendEmail1(String toEmail, String messageHeading, String messageBody) {
Properties props = new Properties();
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.host", "smtp.gmail.com");
props.put("mail.smtp.port", "587");
if (session == null) {
session = Session.getInstance(props,
new javax.mail.Authenticator() {
#Override
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(USERNAME, PASSWORD);
}
});
}
try {
Message message = new MimeMessage(session);
message.setFrom(new InternetAddress(USERNAME));
message.setRecipients(Message.RecipientType.TO,
InternetAddress.parse(toEmail));
message.setSubject(messageHeading);
message.setText(messageBody);
Transport.send(message);
System.out.println("Send Successfully");
} catch (MessagingException e) {
throw new RuntimeException(e);
}
}
}

Answer 1

After going through the comment of stdunbar, I created firewall Exceptions for the ports 25, 465 and 587 for google cloud compute engine.
Then everything started working fine.
Now emails are been sent successfully.

Answer 2

If you are using App Engine, you can use JavaMail which uses the Mail API. Alternatively, if you are using Compute Engine, then we recommend that you use another mail service like Mailgun or Sendgrid.