I have worked with MDaemon, QMail and MS-Exchange as mail server  to use in the purpose you want. There is no difference between them. For Windows, I think MS-Exchange has some good services, but it needs more resources over MDaemon.
MS-Exchange has enough documents and tutorials to help you but MDaemon hasn't it (Or I didn't find).
If you are using Unix QMail is a good and mature mail server.