Find here information about the Outbox service in CAP Java.
Usually the emit of messages should be delayed until the main transaction succeeded, otherwise recipients will also receive messages in case of a rollback. To solve this problem, an outbox can be used to defer the emit of messages until the success of the current transaction.
In-Memory Outbox (Default)
The in-memory outbox is used per default and the messages are emitted when the current transaction is successful. Until then, messages are kept in memory.