Comment 1 for bug 918414

I have been thinking about that recently. The first thing to do would be to
allow a directory of (single message) mail files to be viewed as a folder.
I will call them "directory folders" for the time being.

The first time you load a directory folder it would be time-consuming
because a directory is not a mail server and you can't ask it to give you
just the message headers. But, once the folder has been craeted, viewing
messages should be fairly efficient.