Well, if your server isn't under too much load, then it will be able to send emails for you. There are literally dozens of email servers to choose from.
The most popular *NIX server seems to be
Exim, but I don't think they do a Windows distribution.
Apache James is good, and is widely documented, but it is ultimately up to you. Is there not an email server provided with Windows by default?
Anyway, after some Googling I found
this.