Use your linux mailing system offline, receive mail for multiple users with only one email address, and without being 24-24 online on the net. If you are unable to pay a direct line to stay online for 24-24 and still want your users to receive mail on your linux box; as well not pay for a multi-drop box at your isp, you can use this system using only one email address to divide to your users email addresses. It is as well 24-24 reachable since the server where your account resists will receive the mail.