Plugin to host email discussion groups?

I am searching a plugin that provides a member discussion group (like Google, Yahoo groups) where members can post via email and the email gets automatically forwarded to other members of the same group. I am aware of various newsletter solutions, but they don’t seem to facilitate discussions.

I would need it on a hosted server where PHP and MySQL are available, but not Perl etc.

There are some threads on this forum with the same question – all seem to be many years old and without results. So maybe something has developed since then? Thanks