I have not studied the maildrop filtering language in detail yet, but it seems
as since our mail for virtual accounts is stored under one uid/gid, the users
could write the filter rules, which could potentialy do anything in the maildirs
of the other users. Is that true ? And if yes, is there a way to avoid/limit it
(Besides making every user have his own UID/GID, which kind of defies the idea
of Virtual Mail system).