Yes, when receiving mail (I use Thunderbird v14 or Squirrelmail 1.4), the mailbox structure of ISPconfig 3 with courier is incorrect but functioning correctly. Every other folders become subfolders of INBOX. The structure is:
| - Drafts
| - Sent
| - Archives
| - Junk
| - Trash
The correct normal structure should be:
Please correct it in the next release.