There is no reason it could not use a database, but not that I know of. The email messages end up in a directory in plain text. So for instance if you are running MS Server 2003 with the MS email server setup, the system admin (with the proper permissions) can go in and read your emails with notepad. Same goes for Linux email servers. Maybe Gmail (or another huge service provider) uses a database on the backend, but as far as I know email is just directories and text files.