Inboxes and Outboxes act as gates in your SAP system for all SAP changes moving through the landscape.
When a change reaches an Inbox, appropriate approval emails are sent to required approvers.
The change will not import into the associated system until Inbox Approval is granted.
When a change reaches an outbox, an approval email is sent to the required approvers.
The change will not move out of the associated system until the Oubox approval is granted.
With giving an approval the defined analyzers for this control point are executed.