For example, when you use a fast connection, Office Outlook 2007 copies the header, body, and attachments of an email item from the email server to your computer.
When a slower connection is selected, only headers are automatically downloaded.
However, you do have the option of manually requesting the update.
Additional optimizations are also made to reduce the amount of data sent over the connection.
If Outlook is stuck in Offline mode, see Work offline in Outlook.
Important: When using Outlook with an Office 365 mailbox, we recommend always using Cached Exchange Mode.
Use Cached Exchange Mode to work with items in your Office 365 or Microsoft Exchange Server mailbox even when your network connection is slow or unavailable.
You cannot use Cached Exchange Mode with a POP or IMAP account.
If you work offline, whether by choice or due to a connection problem, your data is still available to you instantly wherever you are.