Am I reading this right. Each of you has a separate e-mail address (Mailbox)hosted from your domain. In which case each person should have a different log on to their own mailbox, not accessible to the others so leaving a copy on the server isn`t necessary.Each should send & receive from their wn designated mailbox.
Most Domain hosting will let the master e-mail account to pick up anything not recognised as an existing e-mail account. ([email protected], webmaster@, mickeymouse@ etc)