Managing control information of a mail server in a databaes gives a lot of flexibility compared to raw text files. But let's be honest for a moment. Most reader of this tutorial won't set up a mail server with thousands of users to make money with. They are just curious what it's like to run a mail server and wanted to learn a great deal. Are you like them? Then you probably just want to manage a domain and a handful of users and don't like to edit database rows through SQL statements, right? Don't despair - there are two ready web interfaces to manage your mail server.
ISPwebAdminI created this web interface in Python using the Pylons web framework for the Lenny tutorial. And it also works on Debian Squeeze. It may take half an hour to set it up because it's not just a bunch of PHP files to throw on a web server. But it has served me well for two years on a production mail server with 10 domains and 1000 users.
Robert Kuntz is working on MailAdm to replace all other tools. Check out a demo version.

Felix (last name unknown has written a fancy and lightweight web interface. See his web site that even contains a live demonstration.

Scott Moody has contributed another simple web interface consisting of just one PHP file that helps you manage your mail server. Visit his web site if you are interested.
An unnamed contributor claims that Scott's script does not work with Squeeze and provides a fixed script.
Ben Clarke also wrote a free and open source web administration interface. You can find his work at GitHub.