how to send email without sender password for feedback form

string name = txt_name.Text;
        string emailfrom = txt_email.Text;
        string subject = txt_subject.Text;
        string ddl_email = DropDownList1.Text;
        string msg = txt_message.Text;
        //string emailid;
        SmtpClient client = new SmtpClient();


        // NetworkCredential loginInfo = new NetworkCredential(emailto, emailpassword);
        MailMessage message = new MailMessage();
        message.From = new MailAddress(emailfrom + '@' + ddl_email, name);
        message.To.Add(new MailAddress("abc@hotmail.com", "name"));
        NetworkCredential cs = new NetworkCredential("abc@hotmail.com", "xyz");
        if (ddl_email == "gmail.com")
        {
            client.Host = "smtp.gmail.com";
            client.Port = 587;
            client.EnableSsl = true;
        }
        else if (ddl_email == "yahoo.com")
        {
            client.Host = "smtp.mail.yahoo.com";
            client.Port = 587;
            client.EnableSsl = false;
        }
        else
        {
            client.Host = "smtp.live.com";
            client.Port = 587;
            client.EnableSsl = false;
        }
        message.Subject = subject;
        message.Body = msg;
        message.IsBodyHtml = true;

        client.UseDefaultCredentials = true;
        client.DeliveryMethod = SmtpDeliveryMethod.Network;
        client.Credentials = cs;
        client.Send(message);