Not Sending mail in Net 4 or Net 4.5

PLEASE HELP
>
> Website was working on the other host. The code is the same, but it does not work on DiscountASP.NET host
>
> Here is the code that I am using. Password is blocked wit xxx
>
> protected void btSend_Click(object sender, EventArgs e)
> { StringBuilder sb=new StringBuilder();
> sb.AppendLine("NoDemo ");
> sb.AppendLine("--------------------- ");
> sb.AppendLine("Salesman: "+tbYourName.Text.Trim());
> sb.AppendLine("Customer: "+tbCustomer.Text.Trim());
> sb.AppendLine("Time In House: "+ddHouseTime.Text.Trim());
> sb.AppendLine("Reason No Demo: "+tbReason.Text.Trim());
>
> try
> {
> MailMessage mail = new MailMessage();
> SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");
>
> mail.From = new MailAddress("[email protected]");
> mail.To.Add(jack.SendEmailsTo("NotDemo"));//this function bring an email address
> mail.Subject = "No Demo for " + tbCustomer.Text.Trim() + " Salesman: " + tbYourName.Text.Trim();
>
> mail.Body =sb.ToString();
>
> SmtpServer.Port = 587;
> SmtpServer.Credentials = new System.Net.NetworkCredential("[email protected]", "XXXXXXX");
> SmtpServer.EnableSsl = true;
>
> SmtpServer.Send(mail);
> lbMessage.Text = "Mail Send";
> }
> catch (Exception ex)
> {
> lbMessage.Text = "Mail NOT Send";
> }
> }