Add MailClient that uses Java Mail API to send emails. Use it instead of Mailgun client.

Mage.Server/src/main/java/mage/server/MailClient.java

@@ -0,0 +1,53 @@
+package mage.server;
+
+import java.util.Properties;
+import javax.mail.Message;
+import javax.mail.MessagingException;
+import javax.mail.Session;
+import javax.mail.Transport;
+import javax.mail.internet.InternetAddress;
+import javax.mail.internet.MimeMessage;
+import mage.server.util.ConfigSettings;
+import org.apache.log4j.Logger;
+
+public class MailClient {
+
+    private static final Logger logger = Logger.getLogger(Main.class);
+
+    public static boolean sendMessage(String email, String subject, String text) {
+        if (email.length() == 0) {
+            logger.info("Email is not sent because the address is empty");
+            return false;
+        }
+        ConfigSettings config = ConfigSettings.getInstance();
+
+        Properties properties = System.getProperties();
+        properties.setProperty("mail.smtps.host", config.getMailSmtpHost());
+        properties.setProperty("mail.smtps.port", config.getMailSmtpPort());
+        properties.setProperty("mail.smtps.auth", "true");
+        properties.setProperty("mail.user", config.getMailUser());
+        properties.setProperty("mail.password", config.getMailPassword());
+
+        Session session = Session.getDefaultInstance(properties);
+
+        try{
+            MimeMessage message = new MimeMessage(session);
+            message.setFrom(new InternetAddress(config.getMailFromAddress()));
+            message.addRecipient(Message.RecipientType.TO, new InternetAddress(email));
+            message.setSubject(subject);
+            message.setText(text);
+
+            Transport trnsport;
+            trnsport = session.getTransport("smtps");
+            trnsport.connect(null, properties.getProperty("mail.password"));
+            message.saveChanges();
+            trnsport.sendMessage(message, message.getAllRecipients());
+            trnsport.close();
+
+            return true;
+        }catch (MessagingException ex) {
+            logger.error("Error sending message to " + email, ex);
+        }
+        return false;
+    }
+}