There are a few restrictions on distribution of the source code for the basic version of the server, which I'll take directly from the code itself:

This source code is subject to limited distribution. You may use it to learn about email services, you may reuse portions of it in your own code. However, you may NOT call it your own, or redistribute it WITHOUT MY PERMISSION. If you make changes to the code and want them to be part of the distribution, please send them to me at:

The above copyright notice must appear in all source modules that use any portion of this code. In short, just give me credit for what I have done to get you this far.