Mail Server

I don't know if this is the right place to post this.

I developed a PHP website that uses HTML Mime Mail for PHP (http://www.phpguru.org/static/mime.mail.html) and it's installed in a Windows 2003 server.

But until now they told me they don't have a mail server installed and installing Exchange isn't an option ($$$).

So, are there any cheap (or free) mail servers for Windows?

Thanks!!!