[CODE]
FileInfo inf = new FileInfo(HttpContext.Current.Server.MapPath(Url));

/*Pur usando inline il file non è aperto dentro il browser ma esternamente in Excel*/
HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("inline; filename=ExportedExcelFile.csv"));

/*Se uso attachment il file viene aperto come allegato Outlook*/
//HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", Url));

HttpContext.Current.Response.ContentType = "application/ms-excel";
HttpContext.Current.Response.AddHeader("Content-Length", inf.Length.ToString());
            
HttpContext.Current.Response.TransmitFile(inf.FullName); 
[/CODE]