I don't know how many people here are into this sort of thing but I've been using VMWare for a while now to test out different pieces of software and such in an enclosed environment so that it doesn't fuck up my production machines. I recently stumbled upon this neat little mail server called Zimbra. It runs on linux and has a great deal of features that are pretty cool. It runs on top of postfix. I set one up but it's down right now. There's a demo on the site that you can look at if you're at all interested. There's an open source edition to download for free and they supply a VMWare appliance to install in your player or server.