[Dovecot] Shared mailboxes in dovecot

[Jay Mobile]

Hi,
i hve a requirement of setting up two folders which should be shared only to 
selected users only. Pls note that my users are virtual and reside on mysql db. 
im using maildir as storage. lets assume user A wants to share a folder named 
shared with user B only. how can i get this done?
Regards 
Jay