Sending email using Gmail

string smtpAddress = "smtp.gmail.com";
            int portNumber = 587;
            bool enableSSL = true;

            string emailFrom = "xyz@gmail.com";
            string password = "myPassword";
            string emailTo = "xyz@yahoo.com";
            string subject = "Hello";
            string body = "Hello, I'm just writing this to say Hi!";

            using (MailMessage mail = new MailMessage())
            {
                mail.From = new MailAddress(emailFrom);
                mail.To.Add(emailTo);
                mail.Subject = subject;
                mail.Body = body;
                mail.IsBodyHtml = true;
                // Can set to false, if you are sending pure text.

                mail.Attachments.Add(new Attachment("C:\\n.txt"));

                using (SmtpClient smtp = new SmtpClient(smtpAddress, portNumber))
                {
                    smtp.Credentials = new NetworkCredential(emailFrom, password);
                    smtp.EnableSsl = enableSSL;
                    smtp.Send(mail);
                }
            }

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.1 Authentication required