SMTP Server requires a secure connection or client

Question

I am having this issue each time when i try to register new users to my web application. Here is the logic.

<connectionStrings>
    <add name="DefaultConnection" connectionString="Data Source=GcobaniM-L\SQLEXPRESS;Initial Catalog=eNtsaRegistration;Integrated Security=True" providerName="System.Data.SqlClient" />
  </connectionStrings>

       public Task SendAsync(IdentityMessage message)
        {
            // Plug in your email service here to send an email.
            var mailMessage = new MailMessage();
            mailMessage.To.Add(new MailAddress(message.Destination));
            mailMessage.From = new MailAddress("[email protected]");
            mailMessage.Subject = message.Subject;
            mailMessage.IsBodyHtml = true;
            mailMessage.Body = message.Body;
            using (var smtp = new SmtpClient())
            {
                var credential = new NetworkCredential
                {
                    UserName = "[email protected]",
                    Password = "***"
                };
                smtp.Host = "smtp.gmail.com";
                smtp.Port = 587;
                smtp.EnableSsl = true;
                smtp.UseDefaultCredentials = false;
                smtp.Credentials = credential;
                smtp.Send(mailMessage);
            }
            return Task.FromResult(0);
        }
    }