Use this code on the Send Button,

using System.Net.Mail;

 public static void SendMailMessage(string from, string to, string bcc, string cc, string subject, string body)
        {
            try
            {
                MailMessage mMailMessage = new MailMessage();
                mMailMessage.From = new MailAddress(from);
                mMailMessage.To.Add(new MailAddress(to));
                if ((bcc != null) && (bcc != string.Empty))
                {
                    mMailMessage.Bcc.Add(new MailAddress(bcc));
                }
                if ((cc != null) && (cc != string.Empty))
                {
                    mMailMessage.CC.Add(new MailAddress(cc));
                }
                mMailMessage.Subject = subject;
                mMailMessage.Body = "" + body + "";
                mMailMessage.IsBodyHtml = true;
                mMailMessage.Priority = MailPriority.High;
                SmtpClient client = new SmtpClient();
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.Host = "your website url";
                client.EnableSsl = false;
                client.Port = 25;
                System.Net.NetworkCredential credentials = new System.Net.NetworkCredential("your mail-id", "your password");
                client.UseDefaultCredentials = true;
                client.Credentials = credentials;
                client.Send(mMailMessage);
            }
            catch (Exception ex)
            {
                HttpContext.Current.Response.Write(ex.Message);
            }
        }

protected void btnSend_Click(object sender, EventArgs e)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append("

Enquiry");
            sb.Append("
");
            sb.Append("Name : " + "" + txtName.Text);
            sb.Append("
");
            sb.Append("Email : " + "" + txtEmail.Text);
            sb.Append("
");
            sb.Append("Phone Number : " + "" + txtPhone.Text);
            sb.Append("
");
            sb.Append("Message : " + "" + txtMessage.Text);
            string EmailBody = sb.ToString();
            SendMailMessage("your mail-id", "receiver mail-id", "", "", "Enquiry", EmailBody);
            Response.Write("");
        }