I guess that's where we disagree. I think you don't have an order by default, you need to explicitly define it, and transmit it, and store it somehow. Which is after all, why it's not true compression. When you account for that metadata, the "compressed" data is not smaller than the original.
In the OP, the cheat was using filenames to store that data. In a tar file, it's using the tar file metadata to store it. In your email, you're storing the email metadata to keep that ordering. In all cases, order is a key thing that you need to explicitly define, transmit, and store. And in all cases, this metadata takes up more space than is saved by the whole scheme.
