Testing mail functionality on a local network possible?

Hi there, I am wondering if it would be possible to send an e-mail inside my production environment without connecting to the internet. My application is running on OSX and I would like to send mail via php to the win2k machine. I was reading something about mailservers but did not really get if this would be possible without connection to the internet. Does anybody know a good article on that, or could give me a hint? Thanx, Andy