How can i change mime type for reportviewer?

Question

i render and extend with reportviewer but but these code extend with old file extension. For example i want to create with .xlsx but it create xls. how can i change default mimeType?

protected void ExportExcel_Click(object sender, EventArgs e)
{
    Warning[] warnings;
    string[] streamids;
    string mimeType;
    string encoding;
    string extension;
    string filename;

    byte[] bytes = ReportViewer1.LocalReport.Render(
       "Excel", null, out mimeType, out encoding,
        out extension,
       out streamids, out warnings);

    filename = string.Format("{0}.{1}", "ExportToExcel", "xls");
    Response.ClearHeaders();
    Response.Clear();
    Response.AddHeader("Content-Disposition", "attachment;filename=" + filename);
    Response.ContentType = mimeType;
    Response.BinaryWrite(bytes);
    Response.Flush();
    Response.End();
}

Answer 1

For Excel 2007 and above the MIME type differs

Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";

Response.AppendHeader("content-disposition", "attachment; filename=" + filename);

Reference : Content Type for xlsx

Also, What is correct content-type for excel files?