[Dovecot] deleting folders containing subfolders with thunderbird (mbox format) bug

[John Bramley]

When using Thunderbird (dovecot-0.99.13-3.FC3) on Fedora connecting to 
dovecot-0.99.13-3.FC3 I am having problems deleting folders which have 
been created with the 'Allow your new folder to contain: Folders only' 
option picked.

The folder appears to get deleted but upon restarting Thunderbird the 
folder still appears to be there but clicking on it I get the error: 
'The current command did not succeed. The mailserver responded: Mailbox 
doesn't exist: <mailbox name>'.

Upon investigation when creating and deleting a folder called 'bilbo' to 
contain subfolders only:

     Thunderbird sends 'create bilbo/' imap command and then
                       'subscribe bilbo/'

     Dovecot creates a directory 'bilbo' and adds 'bilbo/' to the 
.subscriptions file

which all works ok.

Upon trying to delete the folder and confirming that it should be 
deleted Thunderbird sends:
       'delete bilbo/'
dovecot replies
       'OK Delete completed'
Then thunderbird sends
       'unsubscribe bilbo/'
dovecot replies
       'NO Invalid mailbox name'
which Thunderbird ignores and all seems to have gone ok until 
thunderbird is restarted and the folder reappears in the folder list but 
nothing can be done with it.

I believe that if a client sends an 'unsubscribe' command to a mailbox 
that is currently subscribed the imap server should unsubscribe it - 
even if the actual mailbox doesn't exist (unsubscribe and then delete 
seems to work when testing using telnet to port 143 to send imap commands).

Dovecot does allow mailboxes to be unsubscribed if they don't exist if 
they don't have a tailing '/' character (so deleting folders set to 
contain only messages in Thunderbird works ok).

I expect that everything works ok using Maildir mailboxes because then 
there is no need to mark folders containing folders with a '/' because 
all folders can contain messages and folders.

For my own purposes I have hacked the mbox_get_mailbox_name_status 
function in src/lib-storage/index/mbox/mbox-storage.c to add a check to 
see if the mailbox name is already subscribed to and if it is then 
return status = MAILBOX_NAME_EXISTS, before the 'if 
(!mbox_is_valid_create_name(storage, name))' check which is returning 
status = MAILBOX_NAME_INVALID, which seems to work ok for me.

UW-imap works ok

I'm surprised at this bug (or am I doing something completely wrong), 
surely lots of people use Thunderbird with dovecot, do they not create 
sub-folders in folders, or are they all using Maildir format, or do they 
never find the 'Server supports folders that contain sub-folders and 
messages' advanced option so they are never able to create folders 
within folders in the first place?

John.