[Dovecot] Mixing MBOX and MAILDIR

Hello,

I have about 100 mboxes, a few with a lot of mails and others with a few

mails. I have configured dovecot to use maildir as mail format, but I would like to give users the ability to access their old email located in their old mbox. So all the new mail would be in the ~/Maildir/ and their old or archived email in /home/vmail/mboxmail/%Ln

How can I add a namespace to achieve my goal...?

namespace private { separator = / hidden = yes prefix = "#mbox/" location = mbox:/home/vmail/mboxmail/%Ln/ }

Like that...? 

Thanks for any inputs...