As I have been installing my own personal server I came across one piece of software where I couldn't find what I believed to be satisfying functionality. I ordered my server with Windows 2008 and MS SQL 2008 Web Edition. I found hMailServer to be a good, reliable mail server and as a bonus it comes with a web interface for configuring it - but there's no webmail, bummer!
I tried searching around for free webmail implementations but most free ones out there are written in PHP which is not an issue at all my IIS server can run PHP easily...