how to retain size or lengh after postback in the fileupload

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ASP.NET

Hello,

In the page load

if (ViewState["attachemnet1"] == null && flupEmailAttachment.HasFile)
      {
          ViewState["attachemnet1"] = flupEmailAttachment.FileName;
          lblAttachemnt1.Text = flupEmailAttachment.FileName;
      }
      // Next time submit and Session has values but FileUpload is Blank
      // Return the values from session to FileUpload
      else if (ViewState["attachemnet1"] != null && (!flupEmailAttachment.HasFile))
      {
          if (ViewState["attachemnet1"] != null && ViewState["attachemnet1"].ToString() != "")
          {
              lblAttachemnt1.Text = ViewState["attachemnet1"].ToString();


          }
          else
          {
              ViewState["attachemnet1"] = lblAttachemnt1.Text;
              lblAttachemnt1.Text = ViewState["attachemnet1"].ToString();


          }
      }
      // Now there could be another sictution when Session has File but user want to change the file
      // In this case we have to change the file in session object
      else if (flupEmailAttachment.HasFile)
      {
          ViewState["attachemnet1"] = flupEmailAttachment.FileName;
          lblAttachemnt1.Text = flupEmailAttachment.FileName;
      }

and

button clicked

if (ViewState["attachemnet1"] != null)
              {
                  strAttachment = ViewState["strAttachment"].ToString();
                  flupEmailAttachment.PostedFile.SaveAs(Server.MapPath("~/uploads/") + strAttachment);

                  //if (!Directory.Exists(fileSavePath))
                  //    Directory.CreateDirectory(fileSavePath);

                  ////after checking or creating folder it's time to save the file
                  ////fileSavePath = fileSavePath + "//" + ViewState["attachemnet1"].ToString();
                  ////flupEmailAttachment.PostedFile.SaveAs(fileSavePath);

                  //FileStream newFile = new FileStream(fileSavePath + ViewState["attachemnet1"].ToString(), FileMode.Create);

                  //// Write data to the file
                  //byte[] Buffer = (byte[])ViewState["attachemnet1"];
                  //newFile.Write(Buffer, 0, Buffer.Length);

                  //// Close file

                  //newFile.Close();
              }

but when i debug the code file content is zero.
and file sending 0 kb when sending mail