Few month ago I made this very same question and I heard that would be possible. Now I see people saying that it isn't possible.
Here's my problem:
I have ~10,000 users talking in a private mailing list. I don't want have 10,001 copies of each mail, so, I wanted to make 1 common folder where all of them have the same access.
Solution that I got:"If all you need is to deliver a single mail to many users at once, you might consider hardlinking the message into the mailbox - you may lose a little space (never more than one block) as the filename entry in the filesystem will require nominal space, but it's likely to be quite efficient. Symlinking won't use any additional filespace for each link, but will use inodes... I'm not sure whether dovecot will handle a symlink for an actual mail message though - I would assume not. In any case, this will only work properly if you are using maildirs, but then if you're not, why not? ;)
Alternatively, the 1.0 series of dovecot does support shared folders, and I believe per-user flags are supported, though I'd like someone to confirm? Again, this will only work easily on maildirs due to filesystem permissions and such... " Quoted from Peter Fern
So, what's the deal about it?