Are you wanting to host a number of different discussion lists? Or are you just looking for a way to get one discussion list going? If the latter, you don't need to install a program; there are services that will host it for you pretty inexpensively (usually depending on how many mentions of themselves they want to add to each email). If you want to host a number of different lists yourself, yeah, it will be more complicated.

[edited by: Beagle at 2:31 am (utc) on Feb. 5, 2007]

If you mean the SE company versions of email discussion lists, then i would rather not. Yes, I want the potential to run several discussion lists so maybe i just need to shell out the money to get something installed?

Using IMAP functions (php, for example) basic listserv functionality can be programmed from scratch without too much trouble. I was toying around with writing one for some friends of mine. I ran out of time though, and moved on to other projects.

It shouldn't take long to program. This is what you need:

A server with mail that can be checked with IMAP
A scripting language that has IMAP functions
A a scheduling program (apache comes with CRON)
A database (say, msql).

You set an address, say, my_list@myserver.com.
You check the address with a CRON job every 3 minutes or so.
You set up special cases for subject=subscribe/unsubscribe, in which case you add/remove the email in the body of the message to the DB.

In the rest of the cases, you send the email to everyone in the DB for that list. Piece o cake.