I've been re-working on this a bit lately, updating code and adding a few new options and features (like XMPP). I consider it beta, like everything I do, but it should work.
Mailboy is a web based mail server administration tool. It comes with a full "howto" guide, uses commonly available Free Software and if you start from a new Debian Wheezy system, should be easy to set up.
The idea of Mailboy is not to be a "professional email solution", but rather a "friends host friends" tool.
I've had this out since late 2009, before it depended on a specific setup (Workaround.org), so you had to do that, then come back and install Mailboy.
Now I've written up a complete howto from a to z to go with the tool (Mailboy).
This still means that at some point someone needs to install a server. If you can do it, you should, and then host your friends, ask for a contribution (server rental) if needed. I've been doing this since about a decade now.