Mailman is free software for managing electronic mail discussion and e-newsletter lists. Mailman is integrated with the web, making it easy for users to manage their accounts and for list owners to administer their lists. Mailman supports built-in archiving, automatic bounce processing, content filtering, digest delivery, spam filters, and more. See its features page for more details (http://www.gnu.org/software/mailman/features.html)
See Mods Admin for instructions on how to install a Mod.