Cache Exchange Mode provides you with improved experience when you use a Microsoft Exchange Server e-mail account, with a copy of your mailbox stored on your computer, providing quick access to your data, and frequently updated by the mail server.
Should you be working offline, whether by choice or due to a connection problem, your data will still be available to you instantly, wherever you happen to be. If a connection from your computer to the computer running the Exchange server is unavailable, Outlook will switch to a Trying to Connect or Disconnected state. Once the connection is restored, Microsoft Outlook will automatically switch back to a Connected or Connected (Headers) state.
Any changes you make while a connection to the server isn't available are synchronized automatically when a connection becomes available, and you may continue to work while changes are synchronized.