use Parallel::ForkManager;
use File::Copy;
my $fm = Parallel::ForkManager->new(5);

for (@ARGV) {
    $fm->start and next;
    if (system("spamc -c < $_")) {
        (my $newname = $_) =~ s/:.*//;
        move $_, "/home/juerd/Mail/spam/new/$newname" or die $!;
    }
    $fm->finish;
}