You can specify whether Microsoft Outlook should prompt you to choose between working online or offline with your Microsoft Exchange Server account, or always start in online mode when your Exchange mailbox is available.
Note: A Microsoft Exchange Server account is required.
Click the File tab.
Click Account Settings, and then click Account Settings.
On the E-mail tab, click your Exchange account, and then click Change.
Click More Settings.
On the General tab, under When starting, select Automatically detect connection state or Manually control connection state.
Tell me more about these two options
Automatically detect connect state Outlook starts in offline mode if a connection the your Exchange server is not available.
Manually control connection state When Outlook starts, you are prompted to choose whether to work online or offline. This option provides you with the ability to work offline, even if a connection to Exchange is available.
Note: If you have not set up Outlook to work offline and are not using Cached Exchange Mode, none of your Outlook data is available when there is not a connection to Exchange.