Previous version of this library (laravel-imap) was throwing "Mailbox name is not valid mUTF-7" error.
Current php-imap library simply returns an empty folder:

$folder = $client->getFolderByPath('INBOX.Entwürfe');

In our fork of laravel-imap we've fixed it using imap_utf8_to_mutf7() function:
freescout-help-desk/freescout#2793 (comment)