Open the File menu and select Work Offline.
Note that the status bar displays the Offline icon. Create new messages (and reply to existing ones) as usual. Click Send after finishing each message.
Messages you send are stored in the Outbox.
To go back online and send the messages, click the Send/Receive button in the Outlook toolbar.
If you have several messages to review and create, you may prefer to work offline. That way, you can create all the messages, go online, and send them all at once. You might use this method if you do not have a separate connection for your Internet access.
After Messages Are Sent
By default, Outlook goes back offline after sending all the messages in your Outbox.