Cached Exchange Mode provides you with a better experience when you use a Microsoft Exchange Server e-mail account. Cached exchange mode allows a copy of your mailbox to be stored on your computer. This copy provides quick access to your data and is frequently updated with the mail server.
If you work offline, whether by choice or due to a connection problem, your data is still available to you instantly wherever you are. If a connection from your computer to the computer running Exchange server isn't available, Outlook switches to Trying to connect or Disconnected. If the connection is restored, Microsoft Outlook automatically switches back to Connected or Connected (Headers). Any changes you make while a connection to the server isn't available are synchronized automatically when a connection is available. You can continue to work while changes are synchronized.