LuffyyffuL How to do to activate a send mail for all users when a user create a new post ?
I guess you mean a special user, whose posts will be sent to all registered users by mail. This indeed might be usefull, @SHC, a means to send messages to all users with e.g. changes to the terms of usage and having these messages documented in the forum as official announcements for newly registered users.
In practice this right should be assigned to a special user role, and a user with this role will only be used to post these kinds of announcements.
This seems like an interesting proposal for an extension to me.