The inbox and outbox concepts are used in the ActivityPub protocol and in email.
The application receives data which it persists to an inbox table in a database.
Once the data has been persisted another application, process or service can read from the inbox table and use the data to perform an operation which it can retry upon failure until completion, the operation may take a long time to complete.
The inbox pattern ensures that a message was received (e.g. to a queue) successfully at least once.
The outbox pattern ensures that a message was sent (e.g. to a queue) successfully at least once.