This is the last free version. Lightweight freeware version available. Commercial version can handle huge volumes. StarNine's ListSTAR is an automated email processor for the Macintosh that allows you to create and maintain Internet-style mailing lists, automated email response systems, and direct mailing lists. Mailing list server.
Price varies from free up to thousands depending on level of support.
Do not confuse this with Majordomo, the Unix-based list management package. Mailbase is the UK's major electronic mailing list service for research in Higher Education. I'm not sure if this software is available publically. It is a Perl script that allows a user to administer a moderated mailing list. Does not require setup by a system administrator, but does require access to a Unix shell prompt and mail.