I have Mail "Folders" nested several layers deep (up to 8 or 10) and, in this case, I was in a hurry and thought a quick way to find the "Folder" would be to use Spotlight.
I think you would need to upgrade to Lion where you can search within mail for Mailbox names (including Folders). Double-check by using the search field in your version of Mail to see if it shows a result when you search for a Mail folder.
Otherwise, the problem you're having then is it's just not tracking mail "folders" to be found within mail. Even under Lion, the Mail folders don't show under spotlight... only in Mail itself.
I did not understand that a "Folder" in Mail is not actually a Folder. I see the Icon and assume that's what it is. I do not know what "message metadata form" means.
Think of it like folders in other apps like your Safari bookmarks. While it may look like a folder, doesn't necessarily mean it's a folder in the finder or something that can be searched on outside the app itself. By "message metadata form", I was referring to search for an email or an attachment to the email in spotlight and the result sends you to that message in Mail itself rather than sending you to the actual file in the Finder.
I have to take your word on that. I thought I would check (using Command F) just for the educational aspect but could not see, given the apparent options, how I would add system files to the search.
I previously mentioned how to do that and dkmarsh has now followed up with detailed steps that should help, but in the end it'll just show you in the Finder and not it Mail itself where the folder / mbox is.
However, the disconcerting issue now is the fact that Spotlight is not locating files it should be finding....such as Word documents. That is very worrisome.
As was mentioned if the word importer is not installed properly that would affect the ability to search by content of word files. Also make sure spotlight is not blocked form the folders where the documents are stored via the system preferences.
