Make a asp.net mail App in C# with Gmail

I have tried many times to make an email app using gmail. I am truly desperate, I have visited the entire Internet even in other languages but I found nothing.

How can I make a email web app in Asp.net c# using gmail?

This is the last code I applied.

try
{
    MailMessage ms = new MailMessage();
    ms.From = new MailAddress("myemail@gmail.com");
    ms.To.Add("fillocj@hotmail.it");
    ms.Body = txtTexto.Text;
    ms.IsBodyHtml = true;

    SmtpClient sm = new SmtpClient();
    sm.Host = "smtp.gmail.com";

    NetworkCredential nt = new NetworkCredential();

    nt.UserName = "myemail@gmail.com";
    nt.Password = "myPassword";

    sm.UseDefaultCredentials = true;

    sm.Credentials = nt;

    sm.Port = 465;

    sm.EnableSsl = true;
    sm.Send(ms);
    LabelError.Text = "Sent";
}
catch
{
    LabelError.Text = "Error";
}

I always fail over and over again. I tried with port: 25, also with 465 and 587. But any of them works fine. I do not know what the problem is. Please help with this issue.