~/Maildir3% touch dovecot-shared
~/Maildir3% chmod 0660 dovecot-shared
~/Maildir3% MAIL=~/Maildir /usr/local/libexec/dovecot/imap
1 create test
x OK Create completed.
2 logout
~/Maildir3% ls -l .test
drwxrws--- 2 tss tss 4096 2007-10-02 23:10 cur/
-rw-rw---- 1 tss tss    0 2007-10-02 23:10 dovecot-shared