mixing Maildir and mdbox

Hello i'm in the process to architect a new email system. i plan to use dovecot 2.2.9 (debian's wheezy). i would like to use maildir for 2 folders on each account (spam and no-spam) and the rest of the folders stored on mdbox. this should be opaque to my users.

the reason for this, is i want to be able to train my anti-spam tools, but they read maildir or mbox, they don't read mdbox or dbox. but i want the other folders as mdbox (performance, backups, alternate storage)

is there any way?, i prefer if is configurable in advance for all accounts but i could live with something that is done after account is created

thanks!

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