Howtoforge posted a tutorial about installing and configuring Mailman on a Debian Squeeze server with a Postfix mail server.

Mailman is an open-source mailing list manager, i.e., it can be used to manage email discussions and newsletter lists. It is probably the most popular and widely used mailing list manager on the Internet. This tutorial explains how to install and configure Mailman on a Debian Squeeze server with a Postfix mail server.

I do not issue any guarantee that this will work for you!

  How To Install And Configure Mailman (With Postfix) On Debian Squeeze