[exim] Exim forwarding using .forward files and Dovecot

Hello I am having some trouble with my exim .forward file. I want to be
able to filter incoming messages into a certain folder based on their
subject. This seems simple enough and works provided that that the
folder in my inbox already exists, however I want the folders to be
automatically created for me.


My .forward file is shown below when the message arrives it creates the
folder /$home///Maildir/.INBOX.test/ /without any trouble but it is not
however recognised by my IMAP client (Thunderbird).

I think this may be because the server uses dovecot and all the other
IMAP folders have the following files in

dovecot-uidlist dovecot.index dovecot.index.cache dovecot.index.log

When exim creates a new folder these files aren't created and so maybe
dovecot doesn't think they are valid IMAP folders.

Any ideas?

------------------------------------------------------------------------
# Exim filter

if $header_subject: contains "empire" then
save Maildir/.INBOX.test/
endif

------------------------------------------------------------------------
/

Some relevant sections of exim.conf/
------------------------------------------------------------------------
userforward:
driver = redirect
check_local_user
file = $home/.forward
no_verify
no_expn
check_ancestor
allow_filter
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply
directory_transport = address_directory

address_directory:
driver = appendfile
create_directory
maildir_format
delivery_date_add
envelope_to_add
return_path_add
------------------------------------------------------------------------