have to make completely open-source/free network. software suggestions and how to setup a mail server network?

I’ll include a few links below but feel free to use your favorite search engine using the following terms:

open source smtp server

Many projects exist. Just find one that meets your needs (OS support, features, license terms, etc…)

Use either FreeBSD, Ubuntu, or whatever flavour of Linux floats your boat.

I prefer FreeBSD.

Then go ahead and install Postfix, that will allow you to send and receive email (from mail server to mail server). Then you need an additional package that allows your end users to retrieve email, I recommend going with Courier IMAP, you can use Outlook or Outlook Express to retrieve email. Or you can Mozilla which is open source too.

This is all open source and you can get it over the Internet.

Set up a Linux server, I would suggest suse, as it has very good configuration tools and is packaged with the postfix and dovecot servers, along with several others. It also has cirrus sasl security. The whole network can be Linux.

I use Smartpost. It’s an Xmail/Courier-IMAP solution that has a great web frontend for domain and user management. That’s only the real reason why I used it… the frontend manamgent.

Although the project is not being maintained anymore, the site and software used for the project still is, such as Xmail, Courier, etc.

It’s a nice setup for Linux!