Removing unnecessary nested subfolder structure under Inbox in Thunderbird 45.0

Try to disable checkbox "Allow server to override namespace". According to thread on bugzilla, some servers indeed store those special folders under the INBOX. But client should be able to view it "as usual", i.e. at the top lever of hierarchy.

Upd. After short discussion (comments deleted) we've found solution. See "UPDATE 4" section in the question.

Try to create a new profile, and if it looks normal then move the old messages to it and delete the old profile.

These two quite old Mozilla bug reports may have relevant content or workarounds :

• Thunderbird should auto detect the root folder for Imap Account
• Use IMAP namespace response for auto hiding of namespace folder at folder pane

---

As you report that this happens for a new Thunderbird profile and other email clients, the most likely source of the problem is in the IMAP server itself. There is probably no way to change the folder structure, but you could simulate it as described below.

From the Mozilla article IMAP: advanced account configuration :

If your email provider doesn't support creating folders that are a peer to the inbox, one workaround would be to create a child folder somewhere that's normally hidden from view and then create a Saved Search folder (aka virtual folder) whose search criteria selects all messages in that child folder. That virtual folder can be a peer to the inbox. While the messages are still physically stored in the child folder you can use the virtual folder as if it's a real folder. It will just have a different icon in the folder pane.