Thunderbird creates a folder called INBOX on the IMAP server, and also a Trash folder inside it.
I guess it happened when I modified the settings, to move deleted messages to the Trash folder (on the IMAP server). There is already in a folder called Trash on the server.
When I choose Account > Server Settings > When I delete a message: Move it to this folder
I see my IMAP root as Inbox
. I can choose any of the existing folders. But something somewhere goes wrong, and instead of using the Trash
folder on my IMAP root, TB creates a folder named INBOX and tries to access folders inside it.
INBOX
(case-insensitive) is in fact required to exist on an IMAP server.Inbox
, then for some strange reason thinks Inbox is a folder.