New (empty) mailbox can not be opened by IMAP client

Hi,

I have Ajenti V + V Mail working perfectly on my Ubuntu server. Except when I create a new mailbox, my IMAP client can't open it (OS X Mail says "Unable to open this mailbox"). As soon as I send an email to that mailbox, it is available and works normally.

How can I solve that, without sending a dummy email each time a create a mailbox?

Thanks!