I can setup a E-Mail Server within your office
I can setup a Linux Based or a Windows Based mail server.
It collects everyone's email through a single internet connection (you will have to pay for only one email address to your hosting company) and then delivers to the appropriate user depending on who the email was addressed to. Users get their email through the Local Server even if they don't have an internet connection.
You may have an unlimited number of E-Mail addresses for the same cost, even though you will pay for only one address to the hosting company , the other email addresses will be hosted locally on the local office mail server.
The administrator can get a copy of all emails sent and received by every user.
The internal mails are delivered instantly without going through the internet. So internally people can email to each other even when the internet is down.