My code does not send email to Gmail, however it sends to Hotmail

My code for some reason does not send emails to Gmail, well, at least emails do not arrive. This is a college job, I earned the score, so no rush, but this is bugging me, what's the problem? Because I can send to hotmail, but for Gmail I have problems. Is my protocol right? I put here only the base code, however, I'm using a graphical interface (swing) to run the code.

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.sql.Date;
import java.text.DateFormat;
import java.util.Base64;
import java.util.Locale;

import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
/**
 * 
 * @author Joubert Joe Vieira Lellis
 *
 */
public class ProtocoloEmail {

    public String log;


    /**
     * 
     * @param emailBody - Corpo do email - Body of the Email
     * @param emailSubject - Assunto do EMail - Subject of the Email
     * @param emailSender - Remetente do email - Email Sender
     * @param emailRecipient - Destinat�rio do Email - Email Recipiente
     * @param emailHost - HOST (Gmail, Hotmail, Yahoo)
     * @throws IOException
     * @throws UnknownHostException
     */
    public void enviar( String emailBody, String emailSubject, String emailSender,String emailRecipient,String emailHost, String password) throws IOException, UnknownHostException{

        SMTP mail = new SMTP(emailHost);
        // Protocolo - Protocol (Simple Mail Transpor Protocol)

        if (mail != null) {
            if (mail.send(emailSubject , emailBody, emailSender, emailRecipient, password)) {
                log = ("Email Enviado \n Mail Sent");
            } else {
                log = ("Falha ao conectar com servidor SMTP \n Connect to SMTP server failed!");
            }
        }
        System.out.println("Pronto. \n Done.");
    }

/**
 * 
 * @author Joubert Joe Vieira Lellis
 *
 */
    static class SMTP {
        private final static int SMTP_PORT = 587; // Porta padr�o SMTP - Default Port SMTP
        InetAddress mailHost;
        InetAddress localhost;
        BufferedReader in;
        PrintWriter out;

        /**
         * 
         * @param   host Host a ser usado - Host to be used. Ex: (gmail, hotmail, yahoo, etc...)
         * @throws  UnknownHostException Tratamento de exce��o de Host - Host Exception
         */
        public SMTP(String host) throws UnknownHostException {
            mailHost = InetAddress.getByName(host);
            localhost = InetAddress.getLocalHost();
            System.out.println("mailhost = " + mailHost);
            System.out.println("localhost= " + localhost);
            System.out.println("Contrutor SMTP pronto. /n SMTP constructor done\n");
        }

        /**
         * 
         * @param msgEmail      Mensagem contendo Assunto e corpo de email - Mensage includind subject and body of the email.
         * @param from          Quem vai enviar o email - Who gonna send that Email.
         * @param to            Quem est� recebendo o email - Who gonna recieve that email.
         * @return              Booleana para saber se tudo ocorreu bem - Boolean to check if everythings is right.
         * @throws IOException  Poss�veis erros - Possible errors.
         */
        public boolean send(String msgAssunto, String msgEmail, String from, String to, String pass) throws IOException {
        //  SSLSocket smtpSocket;
            Socket smtpSocket;
            InputStream inn;
            OutputStream outt;

        // Criptografia 
            String user = Base64.getEncoder().encodeToString(from.getBytes("utf-8"));
            pass = Base64.getEncoder().encodeToString(pass.getBytes("utf-8"));

        //  smtpSocket = (SSLSocket) ((SSLSocketFactory) SSLSocketFactory.getDefault()).createSocket(mailHost, SMTP_PORT);
            smtpSocket = new Socket(mailHost, SMTP_PORT);

            if (smtpSocket == null) {
                return false;
            }
            inn = smtpSocket.getInputStream();
            outt = smtpSocket.getOutputStream();
            in = new BufferedReader(new InputStreamReader(inn));
            out = new PrintWriter(new OutputStreamWriter(outt), true);
            if (inn == null || outt == null) {
                System.out.println("Failed to open streams to socket.");
                return false;
            }
            String initialID = in.readLine();
            System.out.println(initialID);
            System.out.println("HELO ailton.eng.br");
            out.println("HELO ailton.eng.br");
            out.flush();
            String welcome = in.readLine();
            System.out.println(welcome);
            System.out.println("AUTH LOGIN");
            out.println("AUTH LOGIN");
            out.flush();
            out.println(user);
            out.flush();
            System.out.println(user);
            out.println(pass);
            out.flush();
            System.out.println(pass);

            System.out.println("MAIL From:<" + from + ">");
            out.println("MAIL FROM:<" + from + ">");
            out.flush();

            String senderOK = in.readLine();
            System.out.println(senderOK);

            System.out.println("RCPT TO:<" + to + ">");
            out.println("RCPT TO:<" + to + ">");
            out.flush();
            String recipientOK = in.readLine();
            System.out.println(recipientOK);

            System.out.println("DATA");
            out.println("DATA");
            out.flush();

            out.println("Subject: " +msgAssunto);
            out.flush();
            System.out.println(msgAssunto);

            out.println(msgEmail + "\n.\nQUIT\n");
            out.flush();
            System.out.println(msgEmail);

            System.out.println(".");

            out.flush();
            System.out.println("QUIT");
        //  out.println("QUIT");
            out.flush();
            String acceptedOK = in.readLine();
            String resposta;



            System.out.println(acceptedOK);
            /*
            do{
               resposta = in.readLine();

               System.out.println(resposta);
            }while(resposta != null); 
             */

            return true;
        }

    }

}