Create subfolder UNDER inbox in mail in High Sierra
Someone else posted a question about this but the answer was not entirely correct.
https://discussions.apple.com/thread/2628011
Naming the path Inbox/new folder or inbox/new folder does not work. It will put the folder and it's subfolder in the lower section of mail and not under the inbox. To get this to work you have to capatilize INBOX
INBOX/newfolder
MacBook Pro TouchBar and Touch ID, macOS High Sierra (10.13.6)