How I Do Validate The Correct Format File

[HttpPost, ActionName("Email_Load")]
        public ActionResult Email_Load_confirmed(HttpPostedFileBase file)
        {
            File_Model tz = new File_Model();
            
            try
            {
                if (file != null)
                {
                    file.SaveAs(Server.MapPath("~/App_Data/Uploads/Contacts.xls"));
                    _Stores Stores_ = new _Stores();
                    Basic_Helper _Basic_Helper = new Basic_Helper();
                    var Store = Stores_.Get_Store_Info_Prd(_Basic_Helper.Format_URL(Request.Url.Host.ToString()));
                    if (Store != null)
                    {
                        _Basic_Helper = null;
                        _Site_Info Site_Info = new _Site_Info();
                        string connectionString = "Provider=Microsoft.Jet.OleDb.4.0;Data Source=" + Server.MapPath("~/App_Data/Uploads/Contacts.xls") + ";";
                        connectionString += "Extended Properties=Excel 8.0;";
                        // always read from the sheet1.
                        OleDbCommand myCommand = new OleDbCommand("Select * from [Sheet1$];");
                        OleDbConnection myConnection = new OleDbConnection(connectionString);
                        myConnection.Open();
                        myCommand.Connection = myConnection;
                        OleDbDataReader myReader = myCommand.ExecuteReader();
                        while (myReader.Read())
                        {
                            if (!myReader.GetValue(1).ToString().Equals(""))
                            {
                                Site_Info.Insert_Cust_Det_Newsletter(Store.ID, myReader.GetValue(0).ToString(), myReader.GetValue(1).ToString());
                            }
                        }
                        myReader.Close();
                        myCommand.Cancel();
                        myConnection.Close();
                        myConnection = null;
                        Site_Info = null;
                    }
                    Store = null;
                    Stores_ = null;
                    System.IO.File.Delete(Server.MapPath("~/App_Data/Uploads/Contacts.xls")); 
                }
            }
            catch (Exception ex)
            {
                string s = ex.ToString();
                s = "";
               // Response.Write(ex.ToString());
            }
 return View();
        }

@using (Html.BeginForm("Email_Load", "Marketing", FormMethod.Post, new { enctype = "multipart/form-data" }))
{   

  <table class="a_m_s">  
      <tr>
  <td>File:   </td>
     <td>
 <input type="file" name="file" id="file" data-show-preview="false" style="border: 4px solid rgb(224, 0, 0);
padding: 1px;
color: rgb(255, 255, 255);
background: rgb(85, 85, 85) none repeat scroll 0% 0%; clear:both; margin-top:10px;"></td>
     </tr>
      <tr>
          <td></td>
          <td> <br />
     <input type="submit" id="load" value="Upload File" style=" background-color: #e00000; clear: both; color: #fff; border: 3px solid #e00000; margin-left: 10px;"/></td>
    </tr>
  </table>

 }