I'm just trying to understand your thinking here. The folder is a mail folder as seen in the left column of your mail app?
Yes.
First, I'm not sure why one would be searching for that in the first place, but anyway...
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.
if it is that type of folder, it's not actually a folder in the finder. It's a .mbox which is recognized as a "Mail Mailbox" kind rather than a "Folder". Also since mail is stored in your Library, the Spotlight search will not find items there in raw file terms, but only in message metadata form
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.
If I Find in the Finder and include my system files, I get the .mbox files in my results when searching for my Mail "Folders".
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.
However, it's not a search I would normally use anyway. I've always found Spotlight more than adequate....until now.
I am happy to accept that Spotlight won't find what I mistakenly thought was a "Folder" in Mail. 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.