Hello I'm dovecot bigginer from courier-imap. I used shared maildir in courier like this.
1) create maildir # maildirmake -S /home/shared 2) create maildirshared file # echo 'SHARE /home/shared ' > /etc/courier/maildirshared (use tabcode) 3) edit imapd config file IMAP_UMASK=022 IMAP_SHAREDINDEXFILE=/etc/courier/shared/index in courier, only 3 step work . I read http://wiki.dovecot.org