|The best thing is fork over the money for the exchange book at your local bookstore or online.|
There are a number of things to consider. For example you can have a front end fowarder that faces the internet and securely forwards the email to your exchange server.
You need to understand that spam comes from email servers [which means you were hacked] just like yours, if its not properly secured.
You can do just the internet to exchange but you should setup different ports than the standard to again secure your email server.
Get a book. You will be happy you did.