public string SendEmail(string subject, string body, string sender, string receiver, string filePath = null)
        {

                SmtpClient client = new SmtpClient(Configuration["SmtpClient"]);
                client.Port = Convert.ToInt32(Configuration["SmtpPort"]); //587
                client.UseDefaultCredentials = Convert.ToInt32(Configuration["UseDefaultCredential"]) == 1 ? true : false;
                if (!string.IsNullOrEmpty(Configuration["SmtpUsername"]))
                    client.Credentials = new NetworkCredential(Configuration["SmtpUsername"].Trim(), Configuration["SmtpPassword"].Trim());
                client.EnableSsl = Convert.ToInt32(Configuration["SmtpEnableSSL"]) == 1 ? true : false;
                client.DeliveryMethod = SmtpDeliveryMethod.Network;

                MailMessage mailMessage = new MailMessage();
                mailMessage.From = new MailAddress(sender);
                mailMessage.To.Add(receiver);
                mailMessage.IsBodyHtml = true;
                mailMessage.Subject = subject;

                if (!string.IsNullOrEmpty(filePath))
                {
                    mailMessage.AlternateViews.Add(getEmbeddedImage(filePath, body));
                    Attachment attachments = new Attachment(filePath);
                    //attachments.ContentDisposition.Inline = true;
                    mailMessage.Attachments.Add(attachments);
                }
                else
                {
                    mailMessage.Body = body;
                }
                client.Send(mailMessage);

                return "OK";
         }