You are to simulate a voice mail system. The system has a collection of mailboxes, each of which may be accessed by a four digit extension number (7213 for example). A user of the system may put a message into any existing mailbox. (Since we don't have the hardware to actually record voice mail messages available, for the prototype simply have users type text messages in at the keyboard, after first typing in the extension.)
Any user with a valid mailbox and its password may do any of the following:
An administrator needs to be able to activate and deactivate mailboxes. In addition administrators must be able to copy selected messages. Only administrators should be able to do these tasks.
The system must remember the messages even if the power should fail and the system needs to be restarted. The mail needs to be able to be backed up (and restored).