I agree with Al on file-folders and [homescreen-folders]home-screen-folders.
I also agree with not needing a separate tag for the mail folders (the email tag should be sufficient here).
Number 4 (gallery) are in practice most likely filesystem folders (except when tags would be represented as folders). I don't think this would need a separate tag.
But I'm a bit unsure where a possible synonym "folders" should point to. If the mentioned brain-washing would not have taken place, I'd happily agree on Al's suggestion here as well; but even being a MS-abstainer I must admit: on hearing the term "folder", my first association are directories, followed by email folders, and only after that the homescreen folders -- so I'm unsure about that. One good thing about that synonym would be to save us from a tag with the same name reappearing, though :)