Inbox Folders recognized as Subfolders instead of Folders in the sidebar

Steps to reproduce

1. Subfolders are not shown in a tree structure in my inbox
2. They are shown as Nextcloud.Box instead of Box (child) under Nextcloud (parent)

Expected behaviour

The Inbox folders should appear in a tree hierarchy supporting Subfolders and maybe also Subsubfolders.

Mail app

Mail app version: 0.5.3

Mailserver or service: Namecheap Shared Hosting

Transport security - IMAP: SSL/TLS

Transport security - SMTP: SSL/TLS

Number of accounts: 1

Mail app version build date: (only if you are using a Nightly Build)

Server configuration

Operating system: linux

Web server: Apache 2.2.31

Database: MySQL

PHP version: 5.4.43

Version: 10.0.1 (stable)

Updated from an older version or fresh install: Fresh Install

List of activated apps:
Mail
Contacts
Calendar

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No source files or tests are named. Start by reproducing the folder hierarchy with the reported Mail app setup, then trace how Inbox folder names are classified and rendered in the sidebar. Done means nested folders display as a tree, with Box (child) under Nextcloud (parent), including deeper nesting.