my $domain0 = "$ENV{'HTTP_HOST'}";
if $domain0 == "admin.domain.tld" {
   $err_cfg_dir = "$main::cfg{'GUI_ROOT_DIR'}/default_page";
}
if $domain0 == "admin.domain2.tld" {
  $err_cfg_dir = "$main::cfg{'GUI_ROOT_DIR'}/default_page2";
}