Outlook Email over LAN – HOW?

I have 15 PCs on LAN. None connected to Internet (no dialup or Braoadband). All PCs have MS Outlook (2003) installed.
Without using exchange server or .NET Folder is it possible to exchange emails with the 15 users within the LAN?

All 15 emails can be on the same domain. I want to be able to configure Outlook such that simply clicking ‘send/receive’ button should send/receive emails.