i have problem when i am sending mail.

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C#3.5

I am creating window application. When I am sending a mail, at that time error occur
Cannot sent Message : Failure sending mail.
Can you tell me what is the problem in my code.

try
{
                MailMessage mail = new MailMessage(txtfrom.Text, txtto.Text);
                mail.From = new MailAddress(txtfrom.Text);
                mail.To.Add(txtto.Text);
                mail.Subject = txtsubject.Text;
                mail.Body = txtmess.Text;
                SmtpClient smtp = new SmtpClient();
                smtp.Host = "mail.mycompanyid.net";
                smtp.Port = 25;
                NetworkCredential NetCrd = new NetworkCredential();
                NetCrd.Domain = "ip";
                NetCrd.UserName = "myid";
                NetCrd.Password = "mypass";
                smtp.UseDefaultCredentials = false;
                smtp.Credentials = NetCrd;
                smtp.EnableSsl = true;
                smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
                smtp.Send(mail);
                MessageBox.Show("Your Message Sent Successfully");
            }
            catch (Exception ee)
            {
                MessageBox.Show("Cannot send message: " + ee.Message);
            }