sub check_url {

    # Localize the check_referer flag which determines if user is valid.     #
    local($check_referer) = 0;

    # If a referring URL was specified, for each valid referer, make sure    #
    # that a valid referring URL was passed to FormMail.                     #

    if ($ENV{'HTTP_REFERER'}) {
        foreach $referer (@referers) {
            if ($ENV{'HTTP_REFERER'} =~ m|https?://([^/]*)$referer|i) {
                $check_referer = 1;
                last;
            }
        }
    }
    else {
        $check_referer = 1;
    }

    # If the HTTP_REFERER was invalid, send back an error.                   #
    if ($check_referer != 1) { &error('bad_referer') }
}

##</code><code>##

    local($check_referer) = 0;
    my $refhost = $ENV{'HTTP_REFERER'};
    $refhost =~ s/^.*\/\///g;
    $refhost =~ s/\/.*$//g;
    my $refip = `dnsip $refhost`;
    chomp $refip;
    $refip =~ s/\s+$//g;
    print STDERR "[" . localtime() . "] [formmail referer check] \$ENV{'REMOTE_ADDR'} = $ENV{'REMOTE_ADDR'} [$ENV{'REMOTE_HOST'}] \$ENV{'HTTP_REFERER'} = $ENV{'HTTP_REFERER'} \$refhost = $refhost \$refip = $refip.\n";
    foreach $referer (@referers) {
      ($refip eq $referer) and $check_referer = 1;
    }

    # If the HTTP_REFERER was invalid, send back an error.                   #
    if ($check_referer != 1) { &error('bad_referer') }