For the last 20 years I have supported various types of mailing lists software for clients wishing to communicate easily with a group of users.   I started many years ago with Majordomo and then moved to using Mailman (version 2.1.14 has just being released and Version 3.0 in alpha testing).  

Mailman is still one of the best pieces of mailing list software out there today for people wishing to simply send their messages by email, without any fancy modern day interfaces.   It is easy to set up and interfaces with all of the major MTAs (mail transport agents) hosted on Unix (or Linux) servers out there today.   Once setup it is a simple matter for an administrator to add a mailing list and then add subscribers, or have interested parties add themselves to the mailing list.    Once on a Mailman list all one has to do is to send an email address to the list address  such as listname@example.com and the email will get copied out to all the members of the mailing list.    Any members can then reply and the discussion starts.