When Outlook is online, email messages you send are sent immediately and a check for new email messages occurs on a regular interval. For some accounts, such as Exchange or Hotmail accounts, you see new messages immediately as they arrive. However, sometimes you might not want to work online. For example, when you want to reduce data connection charges, you can switch to offline.
Click Send / Receive > Work Offline.
When Outlook switches between working online and offline, all email accounts are changed.
You know you’re working offline when Work Offline is highlighted on the ribbon or Working Offline appears on the status bar at the bottom of the Outlook window.
When Outlook is offline, you can manually send and receive messages on demand without switching back to working online. Click Send / Receive > Send/Receive All Folders.
Go back online
When you’re ready to work online again, click Send / Receive > Work Offline. The button text doesn’t change, but it’s only highlighted when you’re working offline. Working Offline on the status bar also goes away when you’re working online.