There is this great free mailserver called hMailServer which can be found here. It is very stable and works definately like a charm. There is some awesome documentation and thus a breeze to configure. I wanted to use this free mail server on my SharePoint 2010 development / demo machine but got stuck with two problems to resolve.
Every now and then you run into unexpected SharePoint behavior. The Title field of an item is a 'single line of text' field. In my specific case however this Title field contained a file number. Not a problem at all, BUT you get a really strange sort order when you start to sort numbers as strings. File number 1000 comes before file number 9. This is however expected behavior.