Dear Apricots, please don't discard this solution. I think it's very, very important.
Discussion fora are no substitute for listservs. They serve different functions. If you ask a user to open a browser, navigate, and sign-in every time they want to post a question/comment, it's not going to happen. Even less-so is the chance of another user reading and answering /responding to it.
Consider this: even the best email campaigns have open rates of only 32% and click-rates of 10% or less. Somewhere in-between the openers and the clickers are the emailers. And, there's lots and lots of them. Outlook is already open and on your desktop. Insert address and go.
Of course, if your site doesn't lend itself to this kind of solution, you would simply not opt for it and leave just a discussion forum.
Cheers!
Bradley H. Spurr