protected void ibtnExport_Click(object sender, System.Web.UI.ImageClickEventArgs e)
{
DataSet dsMail = new DataSet();
dsMail = objNews.ExportMailDetails(Request.Form["chkNewsLetter"]);

StringBuilder sbContent = new StringBuilder();

for (int i = 0; i <= dsMail.Tables[0].Rows.Count - 1; i++)
{

for (int j = 0; j <= dsMail.Tables[0].Columns.Count - 1; j++)
{

sbContent .Append(" " + dsMail.Tables[0].Rows[i][j].ToString()+ " ");

}

sbContent .Append("\n");
}

Response.Clear();
Response.AddHeader("content-disposition", "attachment;filename=FileName.doc");

Response.Charset = "";

Response.Cache.SetCacheability(HttpCacheability.NoCache);

Response.ContentType = "application/vnd.word";
Response.Write(sbContent .ToString());

Response.End();

}