This is also possible without MS Exchange.
We use a Linux PC as a website and email server w/in our network.
The Linux (or other) box must be setup to act as a mail server (does not require Exchange) and your Outlook Email account must use this server setting for POP and SMTP servers but it actually works better and faster on the local network because it goes such a short distance and through no (or very few) hops.
We also store the Outlook ".pst" file(s) on a file server (this can be any other PC/server, no necessarily the email server) that is backed up each night so everyone's Outlook profiles are safe.