You'll need to explain more about what's confusing you...
Have you figured out how to send mail in the internet and you're
confused about what you might need to do differently to send it
within your intranet?
Or have you not figured out how to send mail at all?
Or are you asking for the instructions that are specific to your intranet,
as opposed to anyone else's intranet?
The simple answer is: sending mail within an intranet is the same
as sending mailing with the internet. See the FAQ, samples, etc., for
instructions.